[exporter/datadogexporter] Add support for custom log source (#35051)

**Description:**
This PR updates
`github.com/DataDog/datadog-agent/comp/otelcol/otlp/components/exporter/logsagentexporter`
to include commit:
DataDog/datadog-agent@09b07eb.
This adds support for setting a custom log source from resource
attribute or log attribute `datadog.log.source`.


**Link to tracking Issue:** <Issue number if applicable>

**Testing:** Tested this locally by sending logs with attribute
`datadog.log.source` and ensuring this was used as the source.

**Documentation:** Updated datadog exporter README.

Author: mackjmr

.chloggen/mackjmr_custom-log-src-support.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: datadogexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add support for setting a custom log source from resource attribute `datadog.log.source`
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35051]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

exporter/datadogexporter/README.md

@@ -72,3 +72,17 @@ To get the service field correctly populated in your logs, you can specify servi
 [alpha]:https://github.com/open-telemetry/opentelemetry-collector#alpha
 [contrib]:https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib
 [AWS]:https://aws-otel.github.io/docs/partners/datadog
+
+### How to add custom log source
+
+In order to add a custom source to your OTLP logs, set resource attribute `datadog.log.source`. This feature requires `exporter.datadogexporter.UseLogsAgentExporter` feature flag to be enabled (now enabled by default).
+
+Example:
+```
+processors:
+  transform/logs:
+    log_statements:
+      - context: resource
+        statements:
+          - set(attributes["datadog.log.source"], "otel")
+```