Consider not hardcoding a hard limit for mutators

See [mutators loaded restricted to at most 10](https://github.com/beyond-all-reason/RecoilEngine/blob/a9bd9de5ccd59cc28c13105f2d3c1249ae3c4f63/rts/Game/GameSetup.cpp#L305-L311).

Consider removing the limit or allowing games to define it.

First question that comes to mind: is there a reason this hard limit would have been imposed at the time?

At least some investigation to understand whether this limit provides some necessary sanity or even is coupled to other things that might break is required.

It's perfectly possible that this was just some oversight on the assumption no game even would have more than 10 mutators (afaik true until the writing of this post) so the code wouldn't require finding the count, but it's good to be safe.

Start in rts/Game/GameSetup.cpp at lines 305-311 and trace how mutators are loaded and counted. Investigate the history and surrounding assumptions behind the limit, including whether removing or making it game-defined could break related behavior. Done means documenting the reason for the limit and implementing a safe resolution if the investigation supports a change.

Written by the indexing model from the issue text.