Dynamically fetch kdeconnect sha, version

I have made utility functions that fetch kde connects latest version and sha256, and use this accordingly. Note that this is not according to homebrew's convention, which is to check for updates with brew livecheck, make pr's to update package versions with brew bump-cask-pr \ bump-formula-pr, and periodically squash git repo history to prevent it from getting too large.

Dynamically fetching these fields makes this cask unsuitable for upstream. It may be worth it to check for package update's in CI. This removes logic from the package definition and relies more on homebrew's dsl and built in tools (mentioned above), which future contributors may be more familiar with.