remove-disabled-packages: add action

[bevanjkay]

This PR adds a modified version of the existing remove-disabled-formulae action that would work across both homebrew-core and homebrew-cask, and be useable in a repository that includes both Formula and Casks.

It may be worthwhile adding an additional feature to pass a variable for the amount of months a package should be disabled before being removed, as there may be a difference in process between homebrew-core and homebrew-cask.

[MikeMcQuaid]

Looks good, thanks @bevanjkay! Could you run brew style --fix over the Ruby here, too?

[bevanjkay]

This now passes style checks for this directory locally

brew style --fix remove-disabled-packages
Inspecting 2 files
..

2 files inspected, no offenses detected

and is also still functional, tested on my own tap.

[MikeMcQuaid]

Thanks @bevanjkay!

[Bo98]

Can you change homebrew-core to use this and delete remove-disabled-formulae entirely? Seems like we're the only user beyond some homebrew-core forks (which are their responsibility to rebase).