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

…c locking policy

docs/GITHUB_PROCESS.md

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+# Automatically Locking Issues and Pull Requests
+Inactive issues and pull requests in Angular repos are automatically locked after 30 days.
+
+Issues and pull requests are locked when both of the following are true:
+- In a closed state
+- No activity for 30 or more days
+
+Automatically locking inactive issues and pull requests allows for Angular's project maintainers to prioritize and focus on active work in our projects.
+
+#### I want to comment on an issue/pull request that was locked, what should I do?
+When an issue has been closed and inactive for over 30 days, the original context has likely become outdated. If you are encountering a similar or related issue in the current version, please open a new issue and provide up-to-date reproduction instructions.