Add "Random AI" bot option

[netnazgul]

Pretty much self-explanatory. Ability to not bother with AI type selection and just allow any of available AIs in the list be picked on the game start.

The issue was raised several times around in forums/chats/reddit, but don't know whether it's a duplicate here, haven't found it.

[jualtmey]

I implemented this one in this PR here #15713.

[Adamer64]

Aww, didn't check here since I started working on it. Too bad.

[Yovvel]

shouldn't this be closed?

[abcdefg30]

The Pull Requests from above were unfortunately never merged.

[MDBarbier]

I'd like to have a look at this one as the old PR has been closed. I'll get a chance to start over the weekend.

[pchote]

We're going to replace the current AI setup as part of #16634, so it would be wise to leave this until that happens.

[MDBarbier]

We're going to replace the current AI setup as part of #16634, so it would be wise to leave this until that happens.

OK thanks no problem