MIGRATION_A365.md: missing explanation of OTEL_LOG_LEVEL vs A365_OBSERVABILITY_LOG_LEVEL

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Summary

The migration guide (section 12) documents the logging level migration from A365_OBSERVABILITY_LOG_LEVEL to OTEL_LOG_LEVEL, but doesn't explain that these are two independent log systems that control different things.

Issue

Users migrating will see both env vars and not understand which to use or why they exist separately:

Env var	What it controls	Default	Values
OTEL_LOG_LEVEL	OpenTelemetry SDK internals — instrumentation patching, span creation, exporter lifecycle	WARN	ALL, DEBUG, VERBOSE, INFO, WARN, ERROR, NONE
A365_OBSERVABILITY_LOG_LEVEL	A365 distro internals — token acquisition, span batching, export HTTP status, skipped spans	none	none, info, warn, error (pipe-separated combos like info|error)

The migration guide section 12 maps old values to new values but implies OTEL_LOG_LEVEL replaces A365_OBSERVABILITY_LOG_LEVEL. In reality both still exist and serve different purposes. The migration guide should:

1. Explain that OTEL_LOG_LEVEL controls OTel SDK diagnostics (not A365 specific)
2. Explain that A365_OBSERVABILITY_LOG_LEVEL still exists and controls A365-specific diagnostics (token, export, span filtering)
3. Clarify when to use which — e.g., use A365_OBSERVABILITY_LOG_LEVEL=info to debug export failures, use OTEL_LOG_LEVEL=INFO to debug instrumentation issues

References

• Migration guide section 12: https://github.com/microsoft/opentelemetry-distro-javascript/blob/main/MIGRATION_A365.md#12-logging-level-migration
• Source: src/shared/logging/logger.ts (OTEL_LOG_LEVEL)
• Source: src/a365/logging.ts (A365_OBSERVABILITY_LOG_LEVEL)

[github-actions]

cc @hectorhdzg @JacksonWeber @lzchen @MSNev @rads-1996 @jeremydvoss

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verified.