[pipeline] mark module as stable (#13571)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Mark the module go.opentelemetry.io/collector/pipeline as stable.

<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #12831

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: atoulme

.chloggen/pipeline_stable.yaml

@@ -0,0 +1,25 @@
+# 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. otlpreceiver)
+component: pipeline
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Mark module as stable
+
+# One or more tracking issues or pull requests related to the change
+issues: [12831]
+
+# (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:
+
+# 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: [api]

versions.yaml

@@ -23,6 +23,7 @@ module-sets:
       - go.opentelemetry.io/collector/consumer
       - go.opentelemetry.io/collector/extension
       - go.opentelemetry.io/collector/extension/extensionauth
+      - go.opentelemetry.io/collector/pipeline
       - go.opentelemetry.io/collector/processor
       - go.opentelemetry.io/collector/receiver
   beta:
@@ -74,7 +75,6 @@ module-sets:
       - go.opentelemetry.io/collector/pdata/pprofile
       - go.opentelemetry.io/collector/pdata/testdata
       - go.opentelemetry.io/collector/pdata/xpdata
-      - go.opentelemetry.io/collector/pipeline
       - go.opentelemetry.io/collector/pipeline/xpipeline
       - go.opentelemetry.io/collector/processor/processortest
       - go.opentelemetry.io/collector/processor/processorhelper