feat(pull-request-guidelines): update descriptions

[kenji-miyake]

Description

Update the pull request guidelines. Related: https://github.com/orgs/autowarefoundation/discussions/2816#discussioncomment-3505416

Depends on https://github.com/autowarefoundation/autoware-documentation/pull/193.

Pre-review checklist for the PR author

The PR author must check the checkboxes below when creating the PR.

• [x] I've confirmed the contribution guidelines.
• [x] The PR follows the pull request guidelines.

In-review checklist for the PR reviewers

The Reviewers must check the checkboxes below before approval.

• [x] The PR follows the pull request guidelines.

Post-review checklist for the PR author

The PR author must check the checkboxes below before merging.

• [ ] There are no open discussions or they are tracked via tickets.

After all checkboxes are checked, anyone who has write access can merge the PR.

[github-actions[bot]]

Documentation URL: https://autowarefoundation.github.io/autoware-documentation/pr-194/ Modified URLs:

• https://autowarefoundation.github.io/autoware-documentation/pr-194/contributing/pull-request-guidelines/ci-checks/
• https://autowarefoundation.github.io/autoware-documentation/pr-194/contributing/pull-request-guidelines/