Add "Member" option type

[SuperchupuDev]

Right now, we have the user type for options, which lets you select an user, however, this user can be any user, even if they're not in the server. This leads to custom checks on the dev side to know if the user selected is really in the guild, otherwise causing issues on commands where you need a member such as timeout. The member option type would require you to select a member of the server, so there's no need to have custom error messages when the user you selected is not in the guild. Isn't one of the points of slash commands
having built-in validation?

[PlavorSeol]

Alternatively there may be a field to restrict USER option type to members in the guild (server), like there is channel_types for CHANNEL and min_value and max_value for INTEGER and NUMBER.
So basically something like this:

Field	Type	Description
members_in_guild_only?	boolean	if the option is USER type, only members in the guild are allowed