feat(collector): support inline Base64 config via OPENTELEMETRY_COLLECTOR_CONFIG_CONTENT

[fatmcgav]

Adds a new OPENTELEMETRY_COLLECTOR_CONFIG_CONTENT environment variable that
accepts a standard Base64-encoded YAML collector config. The decoded content is
fed into the existing yamlprovider (yaml: URI scheme), so no new provider is
needed.

Resolution order:

1. OPENTELEMETRY_COLLECTOR_CONFIG_URI (existing, unchanged — warns if _CONTENT is also set)
2. OPENTELEMETRY_COLLECTOR_CONFIG_CONTENT (new — Base64-decoded YAML)
3. OPENTELEMETRY_COLLECTOR_CONFIG_FILE (deprecated fallback, unchanged)
4. /opt/collector-config/config.yaml (default)

If Base64 decoding fails an error is logged and the extension falls through to
the next option. NewCollector's signature is unchanged.

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

[linux-foundation-easycla]

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