Make sure mimir and cache are in the same AZ

[Rotfuks]

Motivation

Joe found out, that we have some unnecessary cost center when mimir components are comunicating to cache in another availability zone. The communication for this can be found in this slack thread. Good thing is, @QuantumEnigmaa already fixed it. But we now need to make sure this change is documented.

Todo

•  Document the setup and confiugration that is needed when having the cache in the same AZ as mimir

Outcome

• We know in the future how to make sure there is no resource cost with communication of mimir with caches in other AZs

[QuantumEnigmaa]

Mimir architecture doc updated.