Add length validation to the prefix variable in account infra base

[ocofaigh]

There was an issue reported when someone ran the RAG stack that the prefix value was too long for one of the member DAs (maybe it was roks?).
The problem is by the time it fails in the stack, its already deployed many resources from other DAs, and if you change the prefix value at that point, its going to destroy all resource since the resource group will get renamed.

Can we find out the maximum value the prefix can be across all member DAs and add variable validation to account infra base DA (since its the first DA) to ensure its meet the length that will pass for all DAs