Pre-release handling

[roborourke]

What you want to add

It's not clear how this behaves with pre-releases, so it'd be great to see a documentation update, but the best outcome would be an input for whether or not to include pre-release tags.

Why this is needed

The latest tag someone wants may or may not be a pre-release version, e.g. 0.5.0 vs 1.0.0-beta.1 - which would be returned?

[zischknall]

I just ran into this problem today (what a coincidence), I am trying to use this action for pre-release tags but it does not seem like the grep expression matches pre-release versions.

[roborourke]

I think it does match but I want to the opposite behaviour for my own purposes. Not tested it yet but looks easy to change

[falmanna]

@roborourke @zischknall problem is this is running using -E and this doesn't support lookaheads and lookaheads and lookbehinds.
This should be replaced with -P