[Feature] Fleet: Skip stopped clusters during multi-cluster update in Azure Fleet

**Is your feature request related to a problem? Please describe.**
We are using Azure Fleet to manage updates across multiple AKS clusters (currently more than 17 clusters).

For cost optimization, some clusters are occasionally placed in a stopped state, but they still remain part of the Fleet configuration.

When running a multi-cluster update strategy, the entire update run fails if even one cluster is in a stopped state. Because of this, the update process stops and none of the other active clusters get updated.

This makes the update process fragile and requires manual intervention before running updates.

**Describe the solution you'd like**
During a multi-cluster update run, if Fleet detects that a cluster is in a stopped state, it should skip that cluster and continue the update for the remaining active clusters.

This would ensure:

Updates proceed for running clusters

Stopped clusters do not block the entire update

The process becomes more resilient and automated

**Describe alternatives you've considered**
Describe alternatives you've considered

Currently, the workaround is to:

Manually remove stopped clusters from the update strategy, or

Ensure all clusters are running before starting the update.

However, this is not practical in environments with many clusters and frequent update runs.

**Additional context**
Example scenario:

Fleet contains 17 clusters

2 clusters are stopped

15 clusters are running

Current behavior:

The update run fails because of the stopped clusters

Expected behavior:

Fleet should skip the stopped clusters and continue updating the remaining 15 running clusters