Add support for -m

[wcampbell0x2a]

Many times, I will use git-commit --fixup with -m to remember what I am fixing up, and send more context to the reviewer reading the fixup commit.

Any interest in adding a -m, where the commit message is applied to every commit git-absorb adds?

[tummychow]

i'm on the fence about this. the functionality seems very niche - people who rebase away the fixups before pushing will never use this. furthermore, the only way this can be supported is to add the same string to every single commit, so you can't exactly put a specific message on each one. what's the practical value of adding the same string to all the fixups?

on the other hand, the implementation would be very small, so i guess i'll accept a pr for this. i will not accept a pr for anything that involves opening an editor to set the message. fixed string specified on the cli only