Add gamemode arg to "map" command

[tsa96]

The map command should take a second argument that sets the gamemode the map is loaded in. It should support autocomplete and ideally translate terms like "surf" into the corresponding value in the gamemodes enum.

We've been talking about this internally a lot of already and found the implementation harder than expected, so Panzer has stopped working on it for now, so I'm getting it tracked here. Existing functionality around parsing keyvalues from arguments passed to this command make it quite difficult to alter for Momentum. rio brought up a possible approach in #mom-dev on 26/03/2024 (not linking here, but search we can implement special map command behavior in Discord to find it).

@jason-e do you want to tackle this, seeing as @Panzerhandschuh isn't keen?

[Mac-tf2]

Without the second arguement are we defaulting to map prefix mode?

[tsa96]

I have to admit, whilst we've discussed this several times, I still can't remember what we concluded. The prefix was going to play a role I think, but we were also gonna check the static cache?

@jason-e if you could clarify your suggestions here that'd be great, sorry to bring up again but let's get it written down once and for all