[MM-20061] Add System Admin filter to both LDAP and SAML (#13534)

* promote user to admin upon login

* Add SAML support for admin accounts

* update en.json

* update i18n

* Add tests as per comments

* change function name

* fix config.go

* invalidate cache so its not checking for cache when roles change

* add enable attribute and filter

i18n/en.json

@@ -4118,6 +4118,10 @@
     "id": "ent.ldap.syncronize.search_failure_size_exceeded.app_error",
     "translation": "Size Limit Exceeded. Try checking your [max page size](https://docs.mattermost.com/deployment/sso-ldap.html#i-see-the-log-error-ldap-result-code-4-size-limit-exceeded)."
   },
+  {
+    "id": "ent.ldap.validate_admin_filter.app_error",
+    "translation": "Invalid AD/LDAP Admin Filter"
+  },
   {
     "id": "ent.ldap.validate_filter.app_error",
     "translation": "Invalid AD/LDAP Filter"
@@ -4878,6 +4882,10 @@
     "id": "model.config.is_valid.restrict_direct_message.app_error",
     "translation": "Invalid direct message restriction. Must be 'any', or 'team'"
   },
+  {
+    "id": "model.config.is_valid.saml_admin_attribute.app_error",
+    "translation": "Invalid Admin attribute. Must be in the form 'field=value'"
+  },
   {
     "id": "model.config.is_valid.saml_assertion_consumer_service_url.app_error",
     "translation": "Service Provider Login URL must be a valid URL and start with http:// or https://."