FR: accept -n/--note with amend and display it in evolog

[avamsi]

Rare usecase and it's relatively easy to keep multiple commits and amend later, but I sometimes wish there's a way to name / describe amends (instead of trial and error examining a few entries across a certain time range in evolog / op log).

[yuja]

iirc, there were some discussion about reconstructing evolog/obslog based on operation log. If it becomes a thing, evolog entry will show the operation in which the commit was created, and something like "op log waypoints" #3428 can be used as a note.