[p]warn ask to ban when user not in server

[Ascensionn]

Description of the changes

This is to follow up with what @Flame442 said: "If a disruptive user is leaving before a moderator is able to take action, it may often make sense to consider them a troll and bypass the server's standard warnings track."

Instead of warning them, I check if they are in the discord guild; if they are not, then they will be banned.

Closes #6445

Have the changes in this PR been tested?

Note: the command here is "[p]wasd" because I tested it by implementing a new temporary cog.

[Flame442]

My original comment was not intended to be complete approval of the idea of having this command default to banning the member if they have left the server. I think it could be useful to have it as an option (whether that be by asking if they should be banned as a prompt when [p]warn is used on a member that left, or as a config option that causes [p]warn to ban when used on a member that has left), but I would consider it unexpected to happen automatically without any input from the server owner/mod. My comment was mostly intended to address the fact that this issue is one I would consider a fairly rare one to run into, and one that has a fairly easy manual second step to address it.

Regarding the implementation of this fix, the RawUserIdConverter would be the preferred way to accept both a mention or a user ID, and is the converter used by other parts of the bot with similar behavior (ie, [p]ban).

Additionally, you are currently failing the style checks. Please format your PR with black -l 99 using the instructions in our CONTRIBUTING.MD file.

[Ascensionn]

ok, I can add that as a prompt then. The bot should say "[User]" has left the server, so I cannot warn them. Would you like to ban them instead? [Y/N]". If the mod/owner responds with "Y", [User] will be banned. Else, no action will be taken.

I will submit another PR request with the changes.

[Ascensionn]

*Reminder: the reason I used "[p]wasd" here is because I had to create a new separate cog in order to test for this kind of command. After I finished testing it, I carefully put in the modified parts.

From this image, we can see that the bot eventually timed out after it hasn't received a proper command (either Y or N).

The bot only registers the responses it expects. Otherwise it will not do anything and eventually time out.

[Ascensionn]

Implemented the fixes you have mentioned @Flame442

Here is what happens when you warn the user who is not in the server:

Here is what happens when it times out after 10 seconds.

[Flame442]

If the ban is successful, it should create a modlog case (example).

[Flame442]

Thanks for contributing!