[CLD-7046] Ability to disable self hosted server-side requests to CWS (#26070)

* Add 'Disable' config to CloudSettings to prevent the CWS backend from making calls to the Customer Portal

* Add custom error when disabled

* Make Disable setting cloud_restrictable

* Return 422 instead of 400

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/config.go

@@ -3031,6 +3031,7 @@ type CloudSettings struct {
 	CWSURL    *string `access:"write_restrictable"`
 	CWSAPIURL *string `access:"write_restrictable"`
 	CWSMock   *bool   `access:"write_restrictable"`
+	Disable   *bool   `access:"write_restrictable,cloud_restrictable"`
 }
 
 func (s *CloudSettings) SetDefaults() {
@@ -3054,6 +3055,10 @@ func (s *CloudSettings) SetDefaults() {
 		isMockCws := MockCWS == "true"
 		s.CWSMock = &isMockCws
 	}
+
+	if s.Disable == nil {
+		s.Disable = NewBool(false)
+	}
 }
 
 type ProductSettings struct {