Allow commit_message_options to be passed to pull request creator

[greysteil]

Allows a hash of commit message options to be passed to the pull request creator. The allowed options are:

• signoff_details which works as currently used
• prefix which allows a prefix to be specified
• include_scope which takes a boolean to determine with the dependency's scope should be included in the prefix

The intention is for prefix and include_scope to be allowed keys under commit_message in Dependabot's config files, and for this to provide a robust way for folks to specify that they want to use a particular commit style. A config file might look like:

version: 1
update_configs:
  - package_manager: "ruby:bundler"
    directory: "/"
    update_schedule: "live"
    commit_message:
      prefix: "chore"
      include_scope: true

One deficiency here is that the same prefix will be used for all commits, so this won't help folks who want to specify fix for some commits and build for others. That's a pity, but we can iterate towards a solution there if required.

Another option I've toyed with including but so far excluded is downcase_subject, as some conventions require that the entire first line of the commit message is downcased. That would be easy to add later.

[greysteil]

@feelepxyz I'm most interested in your review of the proposed config file changes. The code here should be fine.

[feelepxyz]

@greysteil config file changes make sense to me! 🙌

[Kocal]

That's awesome, thank you for your work! :)

[greysteil]

OK, let's do this. Will need some work on Dependabot's backend to parse and store those options from config files - I'll get that done today / tomorrow.

[greysteil]

The work is now finished in Dependabot Backend, and I've just pushed updated docs here.

[missjwo]

The link in the last message is broken now.

This is probably the link you now want: https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#commit-message