Allow for multiple implementations to reconcile ServiceBindings in the same cluster

[scothis]

Currently we assume there will only ever be a single reconciler for all ServiceBinding resources within the cluster. While there can only be a single definition of a CRD (and webhook conversion between different version of that resource), we can have different reconcilers take responsibility for reconciling specific resources within the cluster. Currently, we force a user to choose a specific implementation for an entire cluster.

Plugable resources in Kubernetes use a class to distinguish between different providers. For example, IngressClass and StorageClass. We could employ the same pattern for the ServiceBinding

[navidsh]

Discussed during interlock.

[baijum]

I think the implementation *Class pattern is becoming common in Keberetes SIG-sponsored APIs.
Here is another example:
https://gateway-api.sigs.k8s.io/references/spec/#networking.x-k8s.io/v1alpha1.GatewayClass

(Side note: This API also uses x-k8s.io API group)

The above API has multiple implementations, including projects part of CNCF :
https://gateway-api.sigs.k8s.io/references/implementations/#contour

[scothis]

As we move towards a common community implementation of the spec, I think there is less need to support multiple installs concurrently. There should only be a single implementation installed into a given cluster. The *Class approach works for networking and storage because they are inherent extension points for Kubernetes. For us, the meaningful extension point isn't the spec implementation, it is the Provisioned Service duck type and to a lesser extent the Application Projection Mapping.

Keeping this open for now to see what others think, but I suggest we close the issue.

[sbose78]

Agreed, Scott.