Allow regex rules to be stored in a separate repository, specified on the command line

[tarkatronic]

Feature Request

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

When attempting to scan a great number of repos, I don't have a good way of storing a global list of regular expressions to search for.

Describe the solution you'd like

I would like to be able to build a separate git repository consisting exclusively of rules files. Then, have a way to specify on the command line, where that repository exists. Something like

> tartufo --git-rules-repo=git@github.com:tarkatronic/lots-of-rules.git ...

This would clone the specified repo, read in the rules, and use them as supplemental regex checks.