Backport OBE-9476, OBE-9259: HEC source / sink enhancements for EA

[janmejay-s1]

No description provided.

[Copilot]

Pull request overview

Backports Splunk HEC source/sink enhancements, adding support for per-batch dynamic request headers in the Splunk HEC logs sink, improving Splunk HEC source auth/channel handling, and instrumenting the partitioned batcher with batch-count gauges.

Changes:

• Splunk HEC source: token parsing enhancements (Splunk/Bearer), token set handling, and making the request channel optional for raw requests when indexer acknowledgements are disabled.
• Splunk HEC logs sink: adds configurable batch_headers extracted from event fields, partitions batches by these headers, and forwards them as HTTP headers (with request-config headers taking precedence).
• vector-stream: adds open_batches / closed_batches gauges and a test for metric emission.

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/sources/splunk_hec/mod.rs	Updates auth token handling and makes raw channel optional; adjusts raw event enrichment accordingly; adds related tests.
src/sinks/splunk_hec/metrics/request_builder.rs	Initializes new request headers field for metrics requests.
src/sinks/splunk_hec/logs/tests.rs	Adds extensive batching-by-header integration tests for the logs sink.
src/sinks/splunk_hec/logs/sink.rs	Partitions batches by configured header values and extracts header values from events.
src/sinks/splunk_hec/logs/request_builder.rs	Carries partition-extracted headers into HecRequest.
src/sinks/splunk_hec/logs/config.rs	Introduces batch_headers configuration and validation; updates config generation/tests.
src/sinks/splunk_hec/common/util.rs	Plumbs request headers through the HTTP batch service builder; adds tests.
src/sinks/splunk_hec/common/service.rs	Applies dynamic headers to outgoing HTTP requests, with static headers overriding.
src/sinks/splunk_hec/common/request.rs	Extends HecRequest with a headers field.
src/sinks/splunk_hec/common/acknowledgements.rs	Updates ack client request building for the new request signature.
src/sinks/humio/logs.rs	Supplies default batch_headers when mapping Humio config to HEC logs sink config.
src/internal_events/splunk_hec.rs	Adds an internal event for invalid dynamic header values.
lib/vector-stream/src/partitioned_batcher.rs	Adds gauges tracking open/closed batch counts and a related test.
lib/vector-stream/Cargo.toml	Adds metrics and metrics-util dependencies to support the new instrumentation/tests.
Cargo.lock	Updates lockfile for new dependencies.

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