[misc] Add docs acknowledgement check (#4310)

adds a GitHub Actions workflow to enforce documentation requirements for pull requests, ensuring contributors acknowledge whether their changes need documentation updates or provide a link to a corresponding docs PR.

- Adds a new GitHub Actions workflow that validates documentation acknowledgement in PR descriptions
- Updates the PR template to include mandatory documentation checkboxes and URL field
- Implements validation logic to ensure exactly one documentation option is selected and verifies docs PR URLs when provided

.github/pull_request_template.md

@@ -12,6 +12,16 @@
 - [ ] Is a feature enhancement
 - [ ] It is a refactor
 - [ ] Created tests that fail without the change (if possible)
-- [ ] Extended the README / documentation, if necessary
 
 > By submitting this pull request, you confirm that you have read and agree to the terms of the [Contributor License Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md).
+
+## Documentation
+Select exactly one:
+
+- [ ] I added/updated documentation for this change
+- [ ] Documentation is **not needed** for this change (explain why)
+
+### Docs PR URL (required if "docs added" is checked)
+Paste the PR link from https://github.com/netbirdio/docs here:
+
+https://github.com/netbirdio/docs/pull/__