docs(github): enhance pull request template with detailed guidelines and checklist

Signed-off-by: Yurii Serhiichuk <[email protected]>

Author: xSAVIKx

.github/pull_request_template.md

@@ -1,10 +1,39 @@
-Fixes #<issuelink>
+<!--
+Thank you for contributing to the project!
 
-## Changes
+Please make sure to read the `CONTRIBUTING.md` file for our contribution guidelines:
+https://github.com/cloudevents/sdk-python/blob/main/CONTRIBUTING.md
+-->
 
+<!--
+Please provide a clear and concise description of the pull request.
+-->
 
-## One line description for the changelog
+**Related Issue:** #<issue_number>
 
+**Type of change:**
+<!--
+Please select one of the following options and delete the others.
+-->
+- Bug fix (non-breaking change which fixes an issue)
+- New feature (non-breaking change which adds functionality)
+- Breaking change (fix or feature that would cause existing functionality to not work as expected)
+- This change requires a documentation update
+- Other (please describe):
 
-- [ ] Tests pass
-- [ ] Appropriate changes to README are included in PR
+**Description:**
+<!--
+Please include a summary of the change and which issue is fixed.
+Please also include relevant motivation and context.
+List any dependencies that are required for this change.
+-->
+
+---
+
+**Pre-submission checklist:**
+- [ ] I have read the [CONTRIBUTING.md](https://github.com/cloudevents/sdk-python/blob/main/CONTRIBUTING.md) file.
+- [ ] I have signed off my commits using `git commit --signoff`.
+- [ ] I have added tests that prove my fix is effective or that my feature works.
+- [ ] I have updated the documentation (`README.md`, `CHANGELOG.md`, etc.) as necessary.
+- [ ] I have run `pre-commit` and `tox` and all checks pass.
+- [ ] This pull request is ready to be reviewed.