chore: create pull request template (#1129)

* create pull request template
* add CLA to template
* add backport section
Co-authored-by: Homayoon Alimohammadi <[email protected]>

Author: nhennigan

.github/pull_request_template.md

@@ -0,0 +1,29 @@
+## Description
+
+What issue is this PR trying to solve?
+
+## Solution
+
+A clear and concise description of how your changes address the above issue.
+
+## Issue
+
+Include a link to the Github issue number if applicable.
+
+## Backport
+
+Should this PR be backported? If so, to which release?
+
+<!-- Label the PR with `backport release-1.XX` to automatically create a backport once this PR is merged -->
+
+## Checklist
+
+<!-- TODO(Niamh): Update when we decide on this in PR #1113-->
+- [ ] PR title formatted as `type: title`
+- [ ] Covered by unit tests
+- [ ] Covered by integration tests
+- [ ] Documentation updated
+- [ ] CLA signed
+- [ ] Backport label added if necessary 
+
+If any item on the checklist is not complete, please provide justification why.