Add client_id support for OpenID (#8579)

- One click OpenID authorization on Login page
- Add client_id help, config keys etc

Thanks to @egorkaru @ihostage for the
original work and testing.

cmd/config/identity/openid/help.go

@@ -26,6 +26,12 @@ var (
 			Description: `OpenID discovery documented endpoint. eg: "https://accounts.google.com/.well-known/openid-configuration"`,
 			Type:        "url",
 		},
+		config.HelpKV{
+			Key:         ClientID,
+			Description: `The client identifier of the authenticating party at the identity provider`,
+			Type:        "string",
+			Optional:    true,
+		},
 		config.HelpKV{
 			Key:         ClaimPrefix,
 			Description: `OpenID JWT claim namespace prefix. eg: "customer"`,