Add OpenTelemetry export and long-term artifact storage

[jusso-dev]

Problem

Prometheus metrics are useful, but operators may want GoUpTime events and browser artifacts in their existing telemetry and storage systems.

Scope

• Emit OpenTelemetry spans/events for checks, incidents, notifications, and worker jobs.
• Add configurable exporters for OTLP endpoint and headers.
• Add object storage backend for browser artifacts using S3-compatible APIs.
• Document retention, cost, and privacy considerations.

Acceptance criteria

• Operators can enable OTLP export with environment variables.
• Check and incident events include useful IDs and status labels.
• S3-compatible artifact storage can be configured instead of local filesystem.
• Telemetry export failure does not break monitoring.
• Tests cover exporter initialization and artifact backend selection.

Dependencies

• Playwright artifacts and retention.

Notes

This issue is part of the GoUpTime product roadmap.