Improve apiserver storage size metric to allow it's graduation

Change name to make it compliant with prometheus guidelines.
Calculate it on demand instead of periodic to comply with prometheus standards.
Replace "endpoint" with "server" label to make it semantically consistent with storage factory

test/instrumentation/documentation/documentation-list.yaml

@@ -3703,6 +3703,7 @@
   subsystem: apiserver
   help: Total size of the storage database file physically allocated in bytes.
   type: Gauge
+  deprecatedVersion: "1.28.0"
   stabilityLevel: ALPHA
   labels:
   - endpoint
@@ -3750,6 +3751,12 @@
   stabilityLevel: ALPHA
   labels:
   - resource
+- name: apiserver_storage_size_bytes
+  help: Size of the storage database file physically allocated in bytes.
+  type: Custom
+  stabilityLevel: ALPHA
+  labels:
+  - server
 - name: transformation_duration_seconds
   subsystem: storage
   namespace: apiserver