[Guardrails] Reduction of bucket ramQuota shouldn't be allowed post creation of maximum number of collections allowed

Steps:

1. Initialise a 1 node cluster running just the kv service.
2. Create a CouchStore bucket with ramQuota=1000MiB.
3. Create 1000 collections in the bucket.
4. Verified that no more collections can be created with the error message '{"errors":{"_":"Maximum number of collections (1000) for this bucket has been reached"}}'
5. Reduced bucket ramQuota to 512MiB.

We shouldn't be allowed to have 1000 collections with just 512MiB ramQuota. Event though it's not mentioned in the PRD, I think enforcing this would prevent the issues like MB-56853 which is one of the reasons we have this guard rail in the first place.