Automatically update and test Homebrew formula during release

[FooBarWidget]

We want to automate this in the release pipeline so that we don't have to do this automatically. We want to update both the open source and the enterprise formula. For the open source formula, we'll want to send a pull request. For the enterprise formula we can just push directly to the enterprise repo.

Note that we should add an option to the release pipeline's Jenkinsfile to allow skipping the automatic updating of the Homebrew formula. Because sometimes the formula requires manual updates, that are more extensive than just updating the URL and SHA.

And before pushing the updated Homebrew formula to a remote repo, be sure to test whether installing the formula actually works.

• We run this install test during the release process, not on every commit (as part of the unit tests) because unlike e.g. passenger_apt_automation, Homebrew formulas are continuously updated by the community and cannot be locked down to a specific version.

Question for the implementor: in order to implement git pushing changes to a remote Git repo, should we create a new Github account for Jenkins? Or should we use one of our personal accounts' security token?

[FooBarWidget]

Question for the implementor: in order to implement git pushing changes to a remote Git repo, should we create a new Github account for Jenkins? Or should we use one of our personal accounts' security token?

We now have a Github bot account.