Update the PR template (#1856)

This pull request updates the `.github/pull_request_template.md` file to
improve the clarity and usefulness of pull request descriptions and
checklists. The changes focus on guiding contributors to provide better
summaries and references, streamlining the checklist, and removing
redundant sections.

Improvements to PR description guidance:

* Added instructions encouraging contributors to provide a more
comprehensive summary, including relevant facts, design choices, and
testing procedures, and clarified how to reference related issues and
pull requests.

Checklist and documentation updates:

* Simplified the checklist by merging unit and integration test items,
and clarified requirements for documenting manual tests and changelog
updates.
* Removed redundant license section and example license header,
streamlining the template for easier use.

<!-- Contributing guide:
https://github.com/open-edge-platform/datumaro/blob/develop/CONTRIBUTING.md
-->

### Summary

<!--
Resolves #111 and #222.
Depends on #1000 (for series of dependent commits).

This PR introduces this capability to make the project better in this
and that.

- Added this feature
- Removed that feature
- Fixed the problem #1234
-->

### How to test
<!-- Describe the testing procedure for reviewers, if changes are
not fully covered by unit tests or manual testing can be complicated.
-->

### Checklist
<!-- Put an 'x' in all the boxes that apply -->
- [ ] I have added unit tests to cover my changes.​
- [ ] I have added integration tests to cover my changes.​
- [ ] I have added the description of my changes into
[CHANGELOG](https://github.com/open-edge-platform/datumaro/blob/develop/CHANGELOG.md).​
- [ ] I have updated the
[documentation](https://github.com/open-edge-platform/datumaro/tree/develop/docs)
accordingly

### License

- [ ] I submit _my code changes_ under the same [MIT
License](https://github.com/open-edge-platform/datumaro/blob/develop/LICENSE)
that covers the project.
  Feel free to contact the maintainers if that's a concern.
- [ ] I have updated the license header for each file (see an example
below).

```python
# Copyright (C) 2025 Intel Corporation
#
# SPDX-License-Identifier: MIT
```

Author: gdlg

.github/pull_request_template.md

@@ -1,37 +1,18 @@
-<!-- Contributing guide: https://github.com/open-edge-platform/datumaro/blob/develop/CONTRIBUTING.md -->
 
-### Summary
+
+<!-- Contributing guide: https://github.com/open-edge-platform/datumaro/blob/develop/CONTRIBUTING.md -->
 
 <!--
-Resolves #111 and #222.
-Depends on #1000 (for series of dependent commits).
+Please add a summary of changes. You may use Copilot to auto-generate the PR description but please consider including any other relevant facts which Copilot may be unaware of (such as design choices and testing procedure).
 
-This PR introduces this capability to make the project better in this and that.
+Add references to the relevant issues and pull requests if any like so:
 
-- Added this feature
-- Removed that feature
-- Fixed the problem #1234
+Resolves #111 and #222.
+Depends on #1000 (for series of dependent commits).
 -->
 
-### How to test
-<!-- Describe the testing procedure for reviewers, if changes are
-not fully covered by unit tests or manual testing can be complicated. -->
-
 ### Checklist
 <!-- Put an 'x' in all the boxes that apply -->
-- [ ] I have added unit tests to cover my changes.​
-- [ ] I have added integration tests to cover my changes.​
-- [ ] I have added the description of my changes into [CHANGELOG](https://github.com/open-edge-platform/datumaro/blob/develop/CHANGELOG.md).​
+- [ ] I have added tests to cover my changes or documented any manual tests.
+- [ ] I have added the description of my changes into [CHANGELOG](https://github.com/open-edge-platform/datumaro/blob/develop/CHANGELOG.md).
 - [ ] I have updated the [documentation](https://github.com/open-edge-platform/datumaro/tree/develop/docs) accordingly
-
-### License
-
-- [ ] I submit _my code changes_ under the same [MIT License](https://github.com/open-edge-platform/datumaro/blob/develop/LICENSE) that covers the project.
-  Feel free to contact the maintainers if that's a concern.
-- [ ] I have updated the license header for each file (see an example below).
-
-```python
-# Copyright (C) 2025 Intel Corporation
-#
-# SPDX-License-Identifier: MIT
-```

.markdownlintignore

@@ -0,0 +1 @@
+pull_request_template.md