Make push:artifact push to multiple git repos

[grasmash]

Proposed changes

Add options to acli push:artifact:

• --destination-git-urls, an array of git urls to push to
• --destination-git-branch, the git branch to push to.

Allow same options to be defined in .acquia-cli.yml:

Alternatives considered

Testing steps

1. Follow the contribution guide to set up your development environment.
2. Clear the kernel cache to pick up new and changed commands: ./bin/acli ckc
3. (add specific steps for this pr)

Merge requirements

• Bug, enhancement, or breaking change label applied
• Manual testing by a reviewer