Adding PR Template (#5130)

* Adding PR Template for agents repo

* Fixing typos

* minor update

* Adding note on how to link ADO WI

Author: tarunramsinghani

.github/pull_request_template.md

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+
+
+**Issue:** <Please describe the issue and add links to issue this is resolving>
+> Note: For adding link to ADO WI see [here](https://learn.microsoft.com/en-us/azure/devops/boards/github/link-to-from-github?view=azure-devops).
+
+**Description:** <Describe your changes here>
+
+**Risk Assesment(Low/Medium/High)**: <Please add the reasoning for the risk assesment>
+
+**Added unit tests:** (Y/N) <Please mark if unit tests were added or updated according changes>
+
+**Additional Tests Performed:** <Add the list of tests Manual or Automated performed for your changes>