feat(collector/receiver): support extra fields in structured JSON function logs

[tomsobpl]

Summary

When a Lambda function emits structured JSON logs (i.e., a log line with a message field), the telemetryapireceiver now extracts any additional fields from the JSON object and maps them to log record attributes.

Previously, only the message field was captured from structured JSON log records. Any extra fields present in the JSON object (e.g., userId, orderId, custom business data) were silently discarded.

{ "message": "order processed", "orderId": "123", "userId": "abc", "level": "info" }

Before:
→ Log record body: "order processed", no extra attributes.

After:
→ Log record body: "order processed", attributes: orderId = "123", userId = "abc".

Changes

• receiver.go: After setting the log record body from the message field, iterate over all remaining keys in the parsed JSON record and add them as log record attributes. The well-known fields (level, message, requestId, timestamp) are skipped since they are already handled separately.
• receiver_test.go: Extended test coverage for JSON logs containing extra fields, covering nested values, arrays, and numeric types.

Notes:

• The attribute key names are taken as-is from the JSON log (no prefix added), keeping the mapping straightforward.
• Values that cannot be converted via pcommon.Value.FromRaw emit a warning and are skipped rather than failing the entire record.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: tomsobpl / name: Tomasz Sobczak (1ad4f56, 34b1730, 56f6141, a211735, d9c75a0)