Add some Drydock documentation plus "Test Configuration" for repository automation

Summary:
Ref T182. Ref T9252.

• Adds a "Test" repository operation that just runs git status to see if things work.
• Adds a button for it in Edit Repository.
• Shows operation status on the operation detail view to make this workflow work a little better.
• Adds a lot of words. Words words words words.

Test Plan:

• Tested repository operation.
• Read words.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T182, T9252

Differential Revision: https://secure.phabricator.com/D14349