v1.5.0: Major improvements

Changelog

• The option to create one single PR or multiple PRs has been added.
  • Note: This only works for update_repos. add_repos will always be created in one single PR.
• The squash_commits is much safer now as it doesn't rebase already pushed commits. You can also choose to squash commits by running the scripts manually.
• The check-variables.lua script has been renamed to helper-functions.lua which includes a few other miscellaneous functions that are used across the repository.
• All repositories are properly updated by using the proper Git commands, which previously did not work.
• A few other minor code cleanup and changes.