[Feature] Install from specified Github Release tag

[alyssadev]

(I started using pho today and it's fantastic, extremely simple and powerful, the github integration in particular is something I love. there's some features I'd like to PR, making issues for them to track them)

Use case: Chatterino made a windows-only release that has no AppImage attached. The previous release has an AppImage but there is no way to specify to use that tag. This feature would extend pho add github --release [latest,prerelease,any] to allow a tag to be provided, e.g pho add github --release v2.4.5 chatterino/chatterino2

Currently:

$ pho add github -r v2.4.5 chatterino/chatterino2
error: invalid github release type

Expected:

$ pho add github -r v2.4.5 chatterino/chatterino2
# installs from specified tag