feat: add metadata

[mfiedorowicz]

This pull request adds support for attaching custom metadata to ingestion requests and entities in the Diode Go SDK. Users can now provide additional context or tracking information at both the entity and request level, and this metadata is preserved across gRPC, dry run, and OTLP export flows. The documentation and test suite have been updated to demonstrate and verify these new capabilities.

Metadata support and API changes:

• Added a new WithIngestMetadata option and supporting types to allow passing metadata (as key-value pairs) with Ingest and IngestProto calls in both GRPCClient and DryRunClient. This metadata is attached to the IngestRequest and serialized as a protobuf struct. [1] [2] [3] [4]
• Updated the client interfaces and implementations to accept variadic options for ingest operations, ensuring backward compatibility. [1] [2]

Documentation improvements:

• Expanded the README.md with detailed usage examples for entity-level and request-level metadata, including how metadata is handled in dry run and OTLP export scenarios. [1] [2] [3]

Testing enhancements:

• Added comprehensive tests to verify metadata handling in Ingest, IngestProto, and dry run flows, including tests for various metadata types (primitives, arrays, nested objects, and edge cases). Ensured that metadata is correctly serialized and included in requests. [1] [2]

Internal codebase updates:

• Imported necessary protobuf packages for struct and JSON serialization to support the new metadata functionality. [1] [2] [3]

These changes make the SDK more flexible and extensible for tracking, auditing, and enriching ingested data with custom attributes.

[github-actions]

Go test coverage

STATUS	ELAPSED	PACKAGE	COVER	PASS	FAIL	SKIP
🟢 PASS	0.23s	github.com/netboxlabs/diode-sdk-go/cmd/diode-replay-dryrun	0.0%	0	0	0
🟢 PASS	1.40s	github.com/netboxlabs/diode-sdk-go/diode	20.7%	286	0	0

Total coverage: 76.6%

[jajeffries]

Overall looks good, but one minor suggestion about the dry run client