Add support for namespace in CosmosDB to optimise tests

[patroza]

When the storeId is set, and allowNamespace is true for this repo, we should override the partitionKey from primary to whatever is set in storeId
and when we do queries, we should always start the query with _partitionKey being primary or the value of storeId.

We have to make sure we run the initialValues for each partitionKey on first use.
Right now we set a marker with id ${SchemaName} to say if we ran the seed already, this would need to be adapted when supporting namespaces.