Merge pull request projectsveltos#273 from gianlucam76/main

A ClusterSet/Set allows to manage a group of clusters and dynamically
select a subset for deployments based on specific criteria.

It offers the following capabilities:

- Selection: Clusters are chosen using a defined clusterSelector;
- Capping: A field named maxReplicas specifies the maximum number of clusters to be
selected from the pool matching the clusterSelector.
- Failover: If a selected cluster becomes unavailable, another cluster from the
matching pool will be automatically chosen to maintain the desired number of active
clusters (up to the maxReplicas limit).

A ClusterProfile can reference a ClusterSet by specifying its name.
A Profile can reference a Set by specifying its name.

The add-ons defined in the ClusterProfile will be deployed only to the
currently selected clusters within the referenced ClusterSet/Set.
This enables dynamic deployment management based on the available and
healthy clusters in the set.

This feature is particularly useful for scenarios where you want to:

Implement active/passive failover:
Create a ClusterSet/Set with maxReplicas: 1 and have it match two clusters in the clusterSelector.
This ensures only one cluster is active at a time.
If the active cluster goes down, the backup cluster will be automatically selected for deployments.

Introduce ClusterSet/Set

Adjust field names for ClusterSet/Set Status fields

In certain case it might be convenient to simply list all clusters
that are part of a ClusterSet/Set without using a cluster selector.

This also makes cluster selection inline with ClusterProfile/Profile.

This PR also removes clusterproxy utility IsClusterReady as duplicate
of IsClusterReadyToBeConfigured.

Add ClusterRefs to ClusterSet/Set

This is a behavior change. Previoulsy, only deleted clusters were not
considered.

…ady-cluster

Matching clusters: only cluster ready to be programmed can be a match

Bump go modules