Added AI Generated code policy

Author: Jibola

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,4 +1,8 @@
-[JIRA TICKET](https://jira.mongodb.org/browse/{ISSUE_KEY})
+<!--
+We do not accept pull requests that are primarily or substantially generated by AI tools (ChatGPT, Copilot, etc.).
+All contributions must be written and understood by human contributors.
+-->
+[JIRA TICKET]
 
 ## Summary
 
@@ -23,7 +27,7 @@
 - [ ] Is all relevant documentation (README or docstring) updated?
 - [ ] Has a MongoDB Employee run [the patch build of this PR](https://github.com/mongodb-labs/ai-ml-pipeline-testing?tab=readme-ov-file#running-a-patch-build-of-a-given-pr)?
 
-### Checklist for Reviewer {@primary_reviewer}
+### Checklist for Reviewer
 
 - [ ] Does the title of the PR reference a JIRA Ticket?
 - [ ] Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)