Change mv-github-commit-prefix to mv-github-commit-message

[LeaVerou]

There is absolutely no reason not to set the whole message, since it's pretty much the same across commits ("Updated foo.json").

[Mayank1728]

hey @LeaVerou ! I would like to contribute

[LeaVerou]

There is absolutely no reason not to set the whole message, since it's pretty much the same across commits ("Updated foo.json").

Although it is different the first time, if the file doesn't already exist ("Created foo.json"). So maybe they should co-exist: if mv-commit-message is set, use that as the whole message, if mv-commit-prefix is set, use that as a prefix, and if they're both set, I guess prefix the former with the latter.

[TusharP05]

Please assign this issue to me if anyone is not Woking on it!