feat: add clusterName label for identify each kubernetes cluster where K8UP is deployed

[lenglet-k]

Summary

We use K8up on multiple clusters. These multiple clusters perform backups of namespaces with the same name. All the metrics are sent in the same pushgateway.

As the metrics have the same labels, we cannot have a detailed overview by cluster. This is the way K8UP currently works, which does not allow metric labels to be overloaded. This PR makes it possible to add a clusterName label per Kubernetes cluster.

So in pushgateway we have backup metrics per Kubernetes cluster and per namespace, which improves monitoring of the execution of backups per Kubernetes cluster.

I essentially added a clusterName variable equivalent to the promUrl variable.

See: #1031

Checklist

For Code changes

• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog
• PR contains the label area:operator
• Commits are signed off
• Link this PR to related issues
• I have not made any changes in the charts/ directory.

[Kidswiss]

Hi

Thanks for the contribution!

I found a typo, the rest looks good to me.

[Kidswiss]

Hi @lenglet-k

Looks like the linter doesn't like some new lines in the check_types.go file. Is it possible that your IDE or Editor doesn't use LF for new lines?