AAP-36315, docs: Add GitHub PR Template (ansible#673)

## Description

This PR introduces a standardized PR template for our repositories to
improve the quality and consistency of pull request submissions. The
template was developed based on:
- Analysis of our successful and problematic past PRs
- Team's Definition of Done requirements
- AWX project's PR template patterns
- Current team needs identified in JIRA AAP-36315

### Key Features:
- Structured sections for description, testing instructions, and DoD
checklist
- Clear distinction between mandatory and optional information
- Integration with our existing workflow (JIRA references, testing
requirements)

## Testing Steps

1. Create a new PR in this repository
2. Verify that the template automatically loads
3. Test filling out both mandatory and optional sections
4. Confirm the template renders correctly in both GitHub and GitLab
interfaces

## References
- JIRA: [AAP-36315](https://issues.redhat.com/browse/AAP-36315)
- Ongoing Template Discussion:
https://redhat-internal.slack.com/archives/C0782UUSZ8X/p1733348812926029
- Mirrors aap-gateway/platform-service-template repo template: 
ansible-automation-platform/aap-gateway#650
ansible/platform-service-template#10

Author: art-tapin

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,62 @@
+# [AAP-XXXXX] Brief Title Describing the Change
+
+## Description
+<!-- Mandatory: Provide a clear, concise description of the changes and their purpose -->
+- What is being changed?
+- Why is this change needed?
+- How does this change address the issue?
+
+## Type of Change
+<!-- Mandatory: Check one or more boxes that apply -->
+- [ ] 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)
+- [ ] Documentation update
+- [ ] Test update
+- [ ] Refactoring (no functional changes)
+- [ ] Development environment change
+- [ ] Configuration change
+
+## Self-Review Checklist
+<!-- These items help ensure quality - they complement our automated CI checks -->
+- [ ] I have performed a self-review of my code
+- [ ] I have added relevant comments to complex code sections
+- [ ] I have updated documentation where needed
+- [ ] I have considered the security impact of these changes
+- [ ] I have considered performance implications
+- [ ] I have thought about error handling and edge cases
+- [ ] I have tested the changes in my local environment
+
+## Testing Instructions
+<!-- Optional for test-only changes. Mandatory for all other changes -->
+<!-- Must be detailed enough for reviewers to reproduce -->
+### Prerequisites
+<!-- List any specific setup required -->
+
+### Steps to Test
+1. 
+2. 
+3. 
+
+### Expected Results
+<!-- Describe what should happen after following the steps -->
+
+## Additional Context
+<!-- Optional but helpful information -->
+
+### Required Actions
+<!-- Check if changes require work in other areas -->
+<!-- Remove section if no external actions needed -->
+- [ ] Requires documentation updates
+  <!-- API docs, feature docs, deployment guides -->
+- [ ] Requires downstream repository changes
+  <!-- Specify repos: django-ansible-base, eda-server, etc. -->
+- [ ] Requires infrastructure/deployment changes
+  <!-- CI/CD, installer updates, new services -->
+- [ ] Requires coordination with other teams
+  <!-- UI team, platform services, infrastructure -->
+- [ ] Blocked by PR/MR: #XXX
+  <!-- Reference blocking PRs/MRs with brief context -->
+
+### Screenshots/Logs
+<!-- Add if relevant to demonstrate the changes -->