Netlify CMS commits that are signed with a verified signature.

**Is your feature request related to a problem? Please describe.**
We try to enforce signed commits on our projects to ensure people are who they say they are when they commit to a repo, but we have to turn this setting off when creating repo's that can be committed to by Netlify cms.

**Describe the solution you'd like**
A way to have signed commits, possibly verified by using gpg keys.

**Describe alternatives you've considered**
Making a specific github account/repo seperate for the cms commits.

**Additional context**
There may be a way to do this currently that I can't think of or find an idea on how to start going about it.