FEATURE: Allow skip_paths config to contain regular expressions

[OsamaSayegh]

@SamSaffron when I was trying to enable snapshots on Discourse, I noticed we don't use Mini Profiler's skip_paths
config but instead use pre_authorize_cb to skip paths:

https://github.com/discourse/discourse/blob/90eeb8f7d95bf8e06adb34acbbb65e2c743e551f/config/initializers/006-mini_profiler.rb#L53-L58

We also use pre_authorize_cb to disable profiling on phones/tablets.

Skipping paths in pre_authorize_cb is problematic for snapshotting because requests that fail the pre_authorize_cb check are eligible for snapshotting, and we do want requests from phones/tablets to be eligible for snapshotting, but we never want (I think) requests to skipped paths to be eligible for snapshotting (e.g. I don't think we want snapshots for assets requests).

The only thing stopping us from using skip_paths is that we want regular expressions but skip_paths currently accepts strings only. This PR allows both strings and regular expressions in skip_paths.

[SamSaffron]

this seems fine to me... thanks!