fix(sources): collect headers for logs in opentelemetry source with use_otlp_decoding set to true (#24307)

* fix(opetelemetry source): collect headers for logs, metrics, traces with/without use_otlp_decoding

* chore: add changelog

* chore: renamed changelog

* chore: removed adding headers to metrics and traces

* chore: Test coverage

* cargo fmt

* Add newline to changelog

* chore: Updated changelog to say that it is for logs only

* chore: fixed clippy warning

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Co-authored-by: Thomas <thomas.schneider@datadoghq.com>