PLT-2170 Send payload in application/json for outgoing webhooks (#3160)

* Send payload in application/json for outgoing webhooks

The Add outgoing webhook UI now has a 'Content-Type' field that allows
to choose between application/x-www-form-urlencoded and
application/json. All outgoing webhooks created before this change will
be considered as x-www-form-urlencoded. There's also a minor change in
the way the outgoing webhook summary is displayed: the 'Callback URLs'
label was missing.

* Fix JS formatting errors

* Increase ContentType field length to 128

store/sql_webhook_store.go

@@ -33,6 +33,7 @@ func NewSqlWebhookStore(sqlStore *SqlStore) WebhookStore {
 		tableo.ColMap("CallbackURLs").SetMaxSize(1024)
 		tableo.ColMap("DisplayName").SetMaxSize(64)
 		tableo.ColMap("Description").SetMaxSize(128)
+		tableo.ColMap("ContentType").SetMaxSize(128)
 	}
 
 	return s
@@ -44,6 +45,7 @@ func (s SqlWebhookStore) UpgradeSchemaIfNeeded() {
 
 	s.CreateColumnIfNotExists("OutgoingWebhooks", "DisplayName", "varchar(64)", "varchar(64)", "")
 	s.CreateColumnIfNotExists("OutgoingWebhooks", "Description", "varchar(128)", "varchar(128)", "")
+	s.CreateColumnIfNotExists("OutgoingWebhooks", "ContentType", "varchar(128)", "varchar(128)", "")
 }
 
 func (s SqlWebhookStore) CreateIndexesIfNotExists() {