feat: add more cluster and machine metrics

Add metrics for enabled cluster features and for various machine properties:

```text
# HELP omni_cluster_features Number of clusters with specific features enabled.
# TYPE omni_cluster_features gauge
omni_cluster_features{feature="disk_encryption"} 1
omni_cluster_features{feature="embedded_discovery_service"} 0
omni_cluster_features{feature="workload_proxy"} 1

# HELP omni_machine_platforms Number of machines in the instance by platform.
# TYPE omni_machine_platforms gauge
omni_machine_platforms{platform="akamai"} 0
omni_machine_platforms{platform="aws"} 0
omni_machine_platforms{platform="azure"} 0
omni_machine_platforms{platform="cloudstack"} 0
omni_machine_platforms{platform="digital-ocean"} 0
omni_machine_platforms{platform="equinixMetal"} 0
omni_machine_platforms{platform="exoscale"} 0
omni_machine_platforms{platform="gcp"} 0
omni_machine_platforms{platform="hcloud"} 0
omni_machine_platforms{platform="metal"} 10
omni_machine_platforms{platform="nocloud"} 0
omni_machine_platforms{platform="opennebula"} 0
omni_machine_platforms{platform="openstack"} 0
omni_machine_platforms{platform="oracle"} 0
omni_machine_platforms{platform="scaleway"} 0
omni_machine_platforms{platform="upcloud"} 0
omni_machine_platforms{platform="vmware"} 0
omni_machine_platforms{platform="vultr"} 0

# HELP omni_machine_secure_boot_status Number of machines in the instance by secure boot status.
# TYPE omni_machine_secure_boot_status gauge
omni_machine_secure_boot_status{enabled="false"} 10
omni_machine_secure_boot_status{enabled="true"} 0
omni_machine_secure_boot_status{enabled="unknown"} 0

# HELP omni_machine_uki_status Number of machines in the instance by UKI (Unified Kernel Image) status.
# TYPE omni_machine_uki_status gauge
omni_machine_uki_status{booted_with_uki="false"} 0
omni_machine_uki_status{booted_with_uki="true"} 10
omni_machine_uki_status{booted_with_uki="unknown"} 0
```

Signed-off-by: Utku Ozdemir <[email protected]>

Author: utkuozdemir

client/api/omni/specs/omni.pb.go

@@ -1227,6 +1227,14 @@ message MachineStatusMetricsSpec {
   uint32 pending_machines_count = 4;
 
   map<string, int32> versions_map = 5;
+  map<string, uint32> platforms = 6;
+  map<string, uint32> secure_boot_status = 7;
+  map<string, uint32> uki_status = 8;
+}
+
+// ClusterMetricsSpec contains metrics about the clusters in the Omni instance.
+message ClusterMetricsSpec {
+  map<string, uint32> features = 3;
 }
 
 // ClusterStatusMetricsSpec provides aggregated state of the number of clusters in not ready phase.