Improve commit process

[GCHQ-Developer-530]

Summary

In our other repos (ic-ui-kit and ic-design-system) we have a pre-commit hook and Commitizen, we should do the same in this repo.

💬 Description

Add a pre-commit hook running prettier, lint, unit tests etc.
Add commitizen following the same pattern as our other repos e.g. fix(root): Fixed subscription page
Update CONTRIBUTING.md with any new steps contributors would have to follow.

💰 Use value

Improve consistency across repos.