SAML: Do not SAML SLO if user is not SAML authenticated (#53418)

* Only SLO user if the user is using SAML

* only one source of truth for auth module info

* ensure SAML is also enabled and not only SLO

* move auth module naming to auth module login package

* use constants in other previously unused spots

pkg/api/api.go

@@ -21,11 +21,14 @@
 //
 // SecurityDefinitions:
 // basic:
-//  type: basic
+//
+//	type: basic
+//
 // api_key:
-//  type: apiKey
-//  name: Authorization
-//  in: header
+//
+//	type: apiKey
+//	name: Authorization
+//	in: header
 //
 // swagger:meta
 package api