Allow to use pre-installed binaries

[borchero]

Motivation

Potentially, tailscale(d?) have been installed via a separate workflow step to manage the Tailscale version via an external tool (e.g. via conda-forge - tailscale, tailscaled). This change allows tailscale/github-action action to simply use these installed binaries rather than forcing the user to download additional binaries.

[borchero]

I just noticed that this would also solve #56 (and supersede #103) as brew install tailscale can be run in a separate step.

[borchero]

FYI, I tested the latest commit in a personal project and it worked nicely.

[jayvdb]

@borchero , could you rebase this

[borchero]

@jayvdb sorry for the delay, finally done :smile:

[jayvdb]

ping @knyar & @patrickod & @willnorris

[haron]

bump, just in case

[borchero]

I'm not really sure what to do to link an already present binary on Windows -- do I need to do anything if it's on the path?

[oxtoacart]

@borchero Apologies, the GitHub action has since migrated to a JavaScript implementation. If you're willing to submit a new PR against that, we'll review it.

One thing I would recommend changing is to just allow specifying the path to the binaries directly as parameters to the action, that way it doesn't matter if they're on the PATH or not. So instead of a download parameter you would have two parameters, existingTailscalePath and existingTailscaledPath or something like that.