Pull Request template

[CerineBnsd]

Summary

Adding a default template for PRs, that will be used in all the repositories of the organization.

Background

Motivation and context

This helps making sure that when opening a PR, the necessary information for reviewers are included.

Proposed solution

Adding a pull_request_template.md in /.github with the content of the template.

Outcome

When opening a new PR, the description is initially filled with the content of the template.

Tests

Affected features

None

Tests plan

None

Additional Details

None.