Add: Pre-commit hooks

[dinhtungdu]

Description of the Change

Add pre-commit hooks and linters to keep the coding style of this project consistent and prevent potential syntax error early.

Alternate Designs

n/a

Benefits

New code is checked before committing.

Possible Drawbacks

We may need to update Github action workflows to match with new changes.

Verification Process

• See new files composer.json and composer.lock in repo.
• Make test changes to simple-page-ordering.php, stage it, commit it, see the pre-commit hooks run.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Closes #40

Changelog Entry

[jeffpaul]

@dinhtungdu can you resolve the conflicts here so we can work to get this and #42 merged?

[dinhtungdu]

@jeffpaul sure! Fixed conflicts.

[helen]

I don't want to do this in a hotfix release, also seems to me if we're adding linting that should be added to CI. Punting to 2.4.

[dinhtungdu]

Closing. We should implement #79 first then rework this PR.