admin: add feedback for require_privmsg commands

[ComputerTech312]

Previously .say, .me and .raw didn't provide feedback in the channel of usage to the user but silently just did nothing.

[dgw]

I think this could go farther.

Several more commands expect to be run in PM, but don't give feedback (e.g. .join, .part, and their tmp counterparts).

Also, the decorator order here now matters. If require_owner or require_admin is silent, it should be the first decorator, last to wrap the function and therefore first to run its checks. Then if the owner/admin check passes, is_privmsg gets a chance to say its error—but not if the user doesn't pass that initial permission check.

That's what we were talking about on IRC, is to have feedback about require_privmsg for these admin commands but only if the user is already authorized to use them. Normal users shouldn't get any response, and the way to accomplish that is to reorder the decorators so perms get checked first.

Huh, unexpectedly it's nice to have a chance to iterate on something without wasting GHA minutes… Wonder if we can treat everyone as a new contributor, even me?

[dgw]

Like I said before (emphasis added):

That's what we were talking about on IRC, is to have feedback about require_privmsg for these admin commands but only if the user is already authorized to use them. Normal users shouldn't get any response

[ComputerTech312]

Changed @plugin.require_admin to be silent if called by an unauthorized user.

Modified a lot since, and I'm now a co-author so someone else should be the approver