Add in RE_* support as feature_flag action

[whardier]

Is your feature request related to a problem? Please describe.

Just a feature request

Describe the solution you'd like

Add in extra actions to test for regular expression matches/searches.

Describe alternatives you've considered

I actually think in many cases the current actions are sufficient. There are always cases where using a regular expression fills the gap and I've already found one where I need to test legacy data to enable a toggle by way of a re.search.

Additional context

See linked PR #692