.github: Add pull request template

.github/pull_request_template.md

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+We follow the Cilium pull request guidelines.
+Please ensure your pull request adheres to the following guidelines:
+
+- [ ] For first time contributors, read [Submitting a pull request]
+- [ ] All code is covered by unit and/or runtime tests where feasible.
+- [ ] All commits contain a well written commit description including a title,
+      description and a `Fixes: #XXX` line if the commit addresses a particular
+      GitHub issue.
+- [ ] If your commit description contains a `Fixes: <commit-id>` tag, then
+      please add the commit author[s] as reviewer[s] to this issue.
+- [ ] All commits are signed off. See the section [Developer’s Certificate of Origin]
+- [ ] Disclose use of machine learning models (including LLMs and other generative AI)
+      in accordance with the [Cilium AI Policy], and indicate the rating using
+      [AI Influence Level].
+      Example: "This PR was prepared with AIL:N. I personally checked X."
+- [ ] Thanks for contributing!
+
+<!-- Description of change -->
+
+Fixes: #issue-number
+
+[AI Influence Level]: https://danielmiessler.com/blog/ai-influence-level-ail
+[Cilium AI Policy]: https://github.com/cilium/community/blob/main/AI-POLICY.md
+[Developer’s Certificate of Origin]: https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#dev-coo
+[Submitting a pull request]: https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#submitting-a-pull-request