avoid overwriting existing dagger install unless force-install is true

[kpenfound]

Fixes #164

This is a breaking change for workflows that rely on the action to install multiple versions of dagger in a single job, but is the most direct approach to make it work out of the box for runners with dagger pre-installed like on depot

[jedevc]

SGTM, but I think we could maybe avoid an error if the version if the right version of dagger is already installed?

[kpenfound]

@jedevc thats the dilemma, right now it doesn't care about the version at all, only whether there is already a dagger binary in the path, and there is no error state. so you have:

preinstalled version	requested version	result without force-install	result with force-install
foo	bar	foo	bar
none	bar	bar	bar
foo	foo	foo (skipped)	foo (downloaded)

my goal was to avoid error states, but we also don't want surprising behavior. The thinking is that if you have dagger pre-installed, you probably expect it to be there. If you want to override that with a specific version, there's a path to do that