docs: create Issue and Pull Request markdown doc, explaining automati…

…c locking policy (angular#32405)

PR Close angular#32405

docs/GITHUB_PROCESS.md

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+<a name="conversation-locking"></a>
+# Automatic conversation locking
+Closed issues and pull requests are locked automatically after 30 days of inactivity. 
+
+## I want to comment on a locked conversation, what should I do?
+When an issue has been closed and inactive for over 30 days, the original context is likely outdated.
+If you encounter a similar or related issue in the current version, please open a new issue and
+provide up-to-date reproduction instructions.
+
+## Why lock conversations?
+Automatically locking closed, inactive issues guides people towards filing new issues with updated
+context rather than commenting on a "resolved" issue that contains out-of-date or unrelated
+information. As an example, someone may comment "I'm still having this issue", but without
+providing any of the additional information the team needs to investigate.