This shows a 'reply' icon in the markup form header. The config to add more
canned responses is `maniphest.canned-responses`.
Note: There is no validation (other than json), so the config is expected to
match the required fields ('name' and 'message')
Note: This shows at all markups, so technically it can be used for patch
review and other places where canned reponses would fit.
Differential Revision: D8034
Dalai Felinto
6139ce1841