Update the PR template (#867)

- Point users to our CONTRIBUTING doc
- Ask contributors for details on how the change was tested
- Request a short description for the CHANGELOG
- Reword the "Licensing" section to be more in-line with established OSS
  practices and specifically reference the Apache 2.0 license of this
  repo.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,29 @@
+<!--
+Please make sure you've read and understood our contributing guidelines;
+https://github.com/aws/aws-for-fluent-bit/blob/mainline/CONTRIBUTING.md
+
+Please provide the following information:
+-->
+
+### Summary
+<!-- What does this pull request do? -->
+
 *Issue #, if available:*
 
-*Description of changes:*
+### Testing
+<!-- How was this tested?
+See https://github.com/aws/aws-for-fluent-bit?tab=readme-ov-file#local-testing
+for instructions on how to run integ tests locally.
+-->
+
+New tests cover the changes: <!-- yes|no -->
+
+### Description for the changelog
+<!--
+Write a short (one line) summary that describes the changes in this
+pull request for inclusion in the changelog.
+-->
 
+### Licensing
 
-By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.
+By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.