[meta] Allow multiple Astarte instances to share the same database

[Annopaolo]

Since the Astarte Kubernetes Operator allows one to have more than one Astarte instance in the same cluster, a natural generalization is to allow multiple Astarte instances to share the same ScyllaDB/Cassandra database. We should add a way to avoid naming conflicts between keyspaces (as Astarte realms), e.g. two different instances having the test realm (or just having the same astarte keyspace :eyes:). A possible solution is adding an Astarte instance ID with which to compute the keyspace name, together with the realm name.

This is a meta issue to keep track of changes in different repos:

• [x] here
• [x] in astarte_core (see https://github.com/astarte-platform/astarte_core/pull/105)
• [x] in astarte_vmq_plugin (see https://github.com/astarte-platform/astarte_vmq_plugin/pull/85)
• [x] in astarte_data_access

[eddbbt]

this also needs to be added https://github.com/astarte-platform/astarte_flow/pull/161

[Annopaolo]

Still open in this repo