feat: add support for multiple Datastores

[synthe102]

Draft implementation of multiple Datastores per TenantControlPlane. Based on the discussion with @prometherion here. I'm opening the PR now to gather feedback.

Todo:

• Write tests
• Improve documentation

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[prometherion]

Have you already figured out how to create the additional Datastore for the additional resources?

If I understood correctly, the API Server will reuse the same CA and client-based certificate for authentication, unless using a plain/non-TLS etcd which is not supported by Kamaji to be registered as Datastore.

[synthe102]

I think I'll use ETCD-Operator with Cert-manager to manage the CA for both the primary and additional ETCDs. I'll then create two Datastore resources for those ETCDs clusters.
I'll try to validate it this week.

[prometherion]

We recently merged a PR on Kamaji ETCD Chart which provides support to Cert Manager, it could be useful.

Edit: we would need to revamp it in order to reuse the same CA and the same server certificate since these are automatically generated every time.