fix(telemetry): warn on unsupported LogPipeline processor types instead of silently skipping

[suvvvv]

What

LogPipelineProcessorType defines GrokParser, and processors of that type can be created via the UI/API — but LogPipelineService.applyProcessor() has no case for it, so it falls through to:

default:
  return logRow;   // silently does nothing

The log passes through unchanged with no signal, so an operator who creates a GrokParser processor has no way to tell why it never transforms anything.

This change logs a clear warning (naming the processor and its type) in the default branch, while still returning the log unchanged:

default:
  logger.warn(
    `LogPipeline processor "${processor.name}" has unsupported processorType "${processor.processorType}" and was skipped. This processor type is not yet implemented and will not transform logs.`,
  );
  return logRow;

This matches the issue's suggested option (surface a warning) without taking on a full grok implementation.

Why

Addresses the "silently does nothing" half of #2515 — unimplemented processor types are now observable in the logs instead of failing quietly on the ingest path.

Tests

LogPipelineService.processLog previously had no unit coverage. This adds it:

• AttributeRemapper — remaps source→target and drops the source; honours preserveSource.
• SeverityRemapper — maps a matching value to severityText/severityNumber; leaves the log unchanged on no match.
• CategoryProcessor — tags the log with the first matching category.
• Unsupported type (GrokParser) — returns the log unchanged and logs a warning (this assertion fails without the source change, confirming it's a real regression guard).
• Filter gating — processors don't run when the pipeline filter doesn't match.
• No mutation — processLog doesn't mutate the input log row.

node node_modules/.bin/jest --config jest.config.json --runInBand ./Tests/Telemetry/LogPipelineService.test.ts
# 8 passed

Prettier-clean; source lints clean.

Refs #2515

[simlarsen]

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