consider refactoring adjustClusterNameIfWildcard method

[p0lyn0mial]

The adjustClusterNameIfWildcard method extracts a cluster name from an etcd key under an object is stored.

At the moment the method uses regular expressions for extracting names.
A suggestion to change it to the following code snippet has been suggested by @stevekuznetsov.
We should consider changing it to the proposed code or something similar if it improves the readability of the code.

 func adjustClusterNameIfWildcard(shard genericapirequest.Shard, cluster *genericapirequest.Cluster, crdRequest bool, keyPrefix, key string) logicalcluster.Name {
    if cluster.Name != logicalcluster.Wildcard || !cluster.Wildcard { // TODO: fix this duplicity, as well
        return cluster.Name
    }
    
    keyWithoutPrefix := strings.TrimPrefix(key, keyPrefix)
    
    var extractCluster func([]string) logicalcluster.Name
    extractor := func(numParts, clusterPart int) func([]string) logicalcluster.Name {
        return func([]string) logicalcluster.Name {
            if len(parts) < numParts {
                klog.Warnf("shard=%s cluster=%s invalid key=%s had %d parts, not %d", shard, cluster, keyWIthoutPrefix, len(parts), numParts)
                return logicalcluster.Name{}
            }
            return logicalcluster.New(parts[clusterPart])
        }
    }
    
    switch {
    case shard.Wildcard():
        // expecting shardName/clusterName/<remainder>
        extractCluster = extractor(3,1)
    case cluster.PartialMetadataRequest && crdRequest:
        // expecting 2699f4d273d342adccdc8a32663408226ecf66de7d191113ed3d4dc9bccec2f2/root:org:ws/<remainder>
        // OR customresources/root:org:ws/<remainder>
        extractCluster = extractor(3,1)
    case cluster.Wildcard():
        // expecting root:org:ws/<remainder>
        extractCluster = extractor(2,0)
    default:
        panic("bad programmer")
    }
    
    parts := strings.Split(keyWithoutPrefix, "/")
    return extractCluster(parts)
}