Block commits by regular expression (BB-9418)
We'd like to block commits that do/don't match a regular expression.
This is a fork of Issue #5658, which is a very popular issue, but it's also pretty tricky to support arbitary custom hooks. Instead, we just want a limited subset of that functionality.
Regular expressions will address 80% of our needs at 20% of the cost.
(For extra credit: let us specify branches by regular expression, too, so if someone checks into a branch named "release-.*" the commit must contain the text "Approved by:")