MON - add "Policy on Russia" gamerule and possibly faction joining

[IlliaYanchuk]

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Quick questions
HOI4 version: 1.14.7
Kaiserreich version: 1.1.4

Describe the specific change you would like:

Add a gamerule that would decide whether MON takes "Russian Friendship" or "On Our Own" focus.

Explain the reasoning behind this actionable change:

More tools for the player to create their own scenarios. It is a lot less niche to implement, since it isn't Ungern only now.

Additional context or comments:

Maybe allow MON to join MA since East Turkestan can already do that with seemingly no complication.
For joining CPS, there's already an issue #24459