aportupgrade command for stable and _git packages

This action goes through all packages (if --all is passed) or the specified packages), checks if there's _git in the pkgver variable, makes a call to the github or gitlab api to get the latest commit for the package and updates the APKBUILD to that _commit and updates to pkgver for the date of that commit. If the package doesn't have _git in the pkgver, it checks via the release-monitoring.org API if there's a new version for that project and if so, updates the APKBUILD.

There's also --all-git and --all-stable which are hopefully self-explaining.

There's also software implemented in various programming languages for various packaging formats (I know mostly just ones for Arch Linux, as I am using that), e.g. https://github.com/simon04/aur-out-of-date implemented in Go. It has checks for a number of upstream sites - see https://github.com/simon04/aur-out-of-date/tree/master/upstream . I don't know how well I can integrate that for Alpine APKBUILDs, if at all. Maybe there are also Python libraries for a similar thing that we can use; this MR is rather just a PoC of "hey, this is possible and it can work!"