Add PR template to the Sources UI repository

[fhlavac]

Description

Created a pull_request_template.md that should help us make sure to follow a standard process for every pull request and to have a to-do list for the author to check before requesting a review.

RHCLOUD-31263

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Screenshots

Before:

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After:

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Checklist ☑️

• [x] PR only fixes one issue or story
• [x] Change reviewed for extraneous code
• [x] UI best practices adhered to
• [x] Commits squashed and meaningfully named
• [x] All PR checks pass locally (build, lint, test, E2E)

• [ ] (Optional) QE: Needs QE attention (OUIA changed, perceived impact to tests, no test coverage)
• [ ] (Optional) QE: Has been mentioned
• [ ] (Optional) UX: Needs UX attention (end user UX modified, missing designs)
• [ ] (Optional) UX: Has been mentioned

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.74%. Comparing base (88348e9) to head (8e16cf0).

:exclamation: Current head 8e16cf0 differs from pull request most recent head b744da0. Consider uploading reports for the commit b744da0 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1206 +/- ## ======================================= Coverage 97.74% 97.74% ======================================= Files 184 184 Lines 3686 3686 Branches 1049 1049 ======================================= Hits 3603 3603 Misses 77 77 Partials 6 6 ```

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