OTel Components: Wrapped config should start from OTel Defaults

[kgeckhart]

Component(s)

Most OTel Collector components

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In the last two upgrades it was noted that most OTel components we wrap start from a "zero" config with no defaults applied. This can cause problems during upgrades when new fields are introduced and instead of us inheriting an upstream default we inject a "zero" value resulting in unexpected behavior.

We should invert all of these so that we start from upstream defaults and override based on our exposed configuration. Doing this isn't a small task I did use AI to research and group these for us to start,

Group 1: pure no-ops (7)

Upstream createDefaultConfig returns &Config{}, so seeding changes nothing. No goldens move. Cheapest way to establish the pattern.

Component	Convert()
otelcol.auth.basic	auth/basic/basic.go:112
otelcol.auth.headers	auth/headers/headers.go:50
otelcol.auth.sigv4	auth/sigv4/sigv4.go:46
otelcol.processor.attributes	processor/attributes/attributes.go:62
otelcol.processor.redaction	processor/redaction/redaction.go:157
otelcol.processor.span	processor/span/span.go:81
otelcol.receiver.fluentforward	receiver/fluentforward/fluentforward.go:63

Group 2: one-line seed (7)

Already build into a named var, so the fix is one line at the top.

mapstructure.Decode into a zero struct, identical shape to the #6842 k8sattributes fix:

Component	Convert()
otelcol.exporter.kafka	exporter/kafka/kafka.go:276
otelcol.receiver.kafka	receiver/kafka/kafka.go:207
otelcol.receiver.vcenter	receiver/vcenter/vcenter.go:404

var result X.Config + field assignment:

Component	Convert()	Note
otelcol.exporter.googlecloud	exporter/googlecloud/googlecloud.go:66	half-done: seeds embedded collector.DefaultConfig() and hardcodes the factory's 12s timeout, but never calls the exporter factory default
otelcol.exporter.googlecloudpubsub	exporter/googlecloudpubsub/googlecloudpubsub.go:71
otelcol.processor.cumulativetodelta	processor/cumulativetodelta/cumulativetodelta.go:109
otelcol.receiver.file_stats	receiver/file_stats/types_convert.go:18

Group 3: small struct literals (19)

Flat upstream configs, 4 or fewer default fields. Batchable 4-6 per PR by kind.

Component	Convert()
otelcol.auth.bearer	auth/bearer/bearer.go:64
otelcol.auth.google	auth/google/google.go:81
otelcol.connector.signaltometrics	connector/signaltometrics/signaltometrics.go:75
otelcol.exporter.faro	exporter/faro/faro.go:48
otelcol.exporter.loadbalancing	exporter/loadbalancing/loadbalancing.go:123
otelcol.exporter.otlp	exporter/otlp/otlp.go:62
otelcol.exporter.otlphttp	exporter/otlphttp/otlphttp.go:73
otelcol.processor.batch	processor/batch/batch.go:74
otelcol.processor.deltatocumulative	processor/deltatocumulative/deltatocumulative.go:79
otelcol.processor.groupbyattrs	processor/groupbyattrs/groupbyattrs.go:59
otelcol.processor.interval	processor/interval/interval.go:79
otelcol.processor.metric_start_time	processor/metricstarttime/metricstarttime.go:85
otelcol.processor.probabilistic_sampler	processor/probabilistic_sampler/probabilistic_sampler.go:78
otelcol.receiver.awsecscontainermetrics	receiver/awsecscontainermetrics/awsecscontainermetrics.go:52
otelcol.receiver.cloudflare	receiver/cloudflare/cloudflare.go:77
otelcol.receiver.faro	receiver/faro/faro.go:57
otelcol.receiver.googlecloudpubsub	receiver/googlecloudpubsub/googlecloudpubsub.go:98
otelcol.receiver.influxdb	receiver/influxdb/influxdb.go:63
otelcol.receiver.zipkin	receiver/zipkin/zipkin.go:58

Group 4: large / nested struct literals (13)

configoptional wrappers, pointer sub-structs, feature-gate-dependent values, side-effecting default helpers. One PR each.

Component	Convert()	Landmine
otelcol.connector.count	connector/count/count.go:119
otelcol.connector.servicegraph	connector/servicegraph/servicegraph.go:151
otelcol.connector.spanmetrics	connector/spanmetrics/spanmetrics.go:190	Histogram unit default reads a feature gate
otelcol.exporter.datadog	exporter/datadog/datadog.go:89	default is datadogconfig.CreateDefaultConfig(), deeply nested
otelcol.exporter.file	exporter/file/file.go:138	Rotation / GroupBy pointer sub-structs
otelcol.exporter.splunkhec	exporter/splunkhec/config/splunkhec.go:266	20 default fields
otelcol.exporter.syslog	exporter/syslog/syslog.go:72
otelcol.extension.jaeger_remote_sampling	extension/jaeger_remote_sampling/jaeger_remote_sampling.go:82	vendored in-tree copy, so the factory is ours
otelcol.receiver.datadog	receiver/datadog/datadog.go:119	nested Intake / Proxy
otelcol.receiver.jaeger	receiver/jaeger/jaeger.go:68	protocols wrapped in configoptional
otelcol.receiver.otlp	receiver/otlp/otlp.go:87	protocols wrapped in configoptional
otelcol.receiver.solace	receiver/solace/solace.go:129	Flow wrapped in configoptional
otelcol.storage.file	storage/file/file.go:199	default calls getDefaultDirectory()

Group 5: behavior fixes (6)

Upstream default sets a non-zero field that Alloy never assigns and doesn't expose, so these already run differently from the collector. Each needs a release note. Two of them need a new Alloy argument, not just a seeded default.

Component	Convert()	Divergence
otelcol.exporter.awss3	exporter/awss3/awss3.go:76	BackOffConfig zero-valued vs configretry.NewDefaultBackOffConfig(); no retry_on_failure block exists
otelcol.exporter.debug	exporter/debug/debug.go:76	QueueConfig zero-valued vs configoptional.Default(NewDefaultQueueConfig()); no sending_queue block exists
otelcol.processor.memory_limiter	processor/memorylimiter/memorylimiter.go:101	MinGCIntervalWhenSoftLimited is 0 vs 10s
otelcol.processor.resourcedetection	processor/resourcedetection/resourcedetection.go:281	ClientConfig never referenced anywhere in the component vs defaultClientConfig()
otelcol.receiver.splunkhec	receiver/splunkhec/splunkhec.go:135	Ack.Path is "" vs /services/collector/ack
otelcol.receiver.awscloudwatch	receiver/awscloudwatch/awscloudwatch.go:66	whole Metrics block zeroed (ControllerConfig, Period, Delay). Confirm inert before writing up: Alloy only exposes logs

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