Update PR template with CodeQL instructions

[santisecco]

Fixes #5196

What changes did you make?

• Modified PR template pull_request_template.md adding CodeQL instructions section. Please refer to the links below. Added more changes to the ones proposed in #5196 after conversation in dev meeting to add further clarity to the PR's instructions.

Why did you make the changes (we will use this info to test)?

• We need developers to check the PR for annotations/comments resulting from CodeQL scanning. This will ensure better Security and Code Quality and give the chance of fixing changes before they are merged.

Screenshots of Proposed Changes To The Website (if any, please do not include screenshots of code changes)

No visual changes to the website itself. Even though, the following links are there to preview the changes to the Pull Request template.

• Previous PR template: https://github.com/hackforla/website/blob/gh-pages/.github/pull_request_template.md

• Updated PR template: https://github.com/santisecco/website/blob/update-pr-template-codeql-5196/.github/pull_request_template.md