Represents the different states that webhooks can be in.
Values:
WEBHOOK_STATE_UNSPECIFIED (0):
Webhook is disabled in the agent and in the
intent.
WEBHOOK_STATE_ENABLED (1):
Webhook is enabled in the agent and in the
intent.
WEBHOOK_STATE_ENABLED_FOR_SLOT_FILLING (2):
Webhook is enabled in the agent and in the
intent. Also, each slot filling prompt is
forwarded to the webhook.