docs: add ADR-0004: Separation of Homeserver Operators
Issue: planning#31
This ADR proposes that the 2 homeservers for government and citizens (ADR-0001 !1) need to be operated by different organizations to make better privacy guarantees.
Consider that !1, !9, and !11 are intertwined ADRs and it may make sense to review all at the same time.
Edited by Kim Brose