Allow specifying bot's response to disabled commands separate for global and server-specific disables

### What component of Red (cog, command, API) would you like to see improvements on?

Core Commands

### Describe the enhancement you're suggesting.

We should be able to separately configure a message for global and server-specific command disabling. Both of the messages would be **global**, but they could differ.
More concretely, the current `command disabledmsg` should be used when the command is globally disabled.
If `command serverdisabledmsg` (this probably isn't the best way to name it) is set, that message is used for commands disabled in specific servers. If it isn't set, `command disabledmsg` continues to be used, as it is today.

### Anything else?

Inspired by #5553 but following an approach closer to what's suggested in the comment:
https://github.com/Cog-Creators/Red-DiscordBot/pull/5553#issuecomment-1019926804.