Rename channel to webhook_id

Author: mpiot

notifier.rst

@@ -139,7 +139,7 @@ integration with these chat services:
 ==========  ================================  ===========================================================================
 Service     Package                           DSN
 ==========  ================================  ===========================================================================
-Discord     ``symfony/discord-notifier``      ``discord://TOKEN@default?channel=ID``
+Discord     ``symfony/discord-notifier``      ``discord://TOKEN@default?webhook_id=ID``
 GoogleChat  ``symfony/google-chat-notifier``  ``googlechat://ACCESS_KEY:ACCESS_TOKEN@default/SPACE?threadKey=THREAD_KEY``
 LinkedIn    ``symfony/linked-in-notifier``    ``linkedin://TOKEN:USER_ID@default``
 Mattermost  ``symfony/mattermost-notifier``   ``mattermost://TOKEN@ENDPOINT?channel=CHANNEL``