PSP: conditional support for generic volume type

When introducing the new "generic" volume type for generic ephemeral
inline volumes, the storage policy for PodSecurityPolicy objects
should have been extended so that this new type is valid only
if the generic ephemeral volume feature is enabled or an
existing object already has it.

Adding the new type to the internal API was also missed.

pkg/security/podsecuritypolicy/util/util.go

@@ -29,6 +29,8 @@ const (
 	ValidatedPSPAnnotation = "kubernetes.io/psp"
 )
 
+// GetAllFSTypesExcept returns the result of GetAllFSTypesAsSet minus
+// the given exceptions.
 func GetAllFSTypesExcept(exceptions ...string) sets.String {
 	fstypes := GetAllFSTypesAsSet()
 	for _, e := range exceptions {
@@ -37,6 +39,8 @@ func GetAllFSTypesExcept(exceptions ...string) sets.String {
 	return fstypes
 }
 
+// GetAllFSTypesAsSet returns all actual volume types, regardless
+// of feature gates. The special policy.All pseudo type is not included.
 func GetAllFSTypesAsSet() sets.String {
 	fstypes := sets.NewString()
 	fstypes.Insert(