Add Eliza Webhook support

[timolegros]

Description

We support Slack, Discord, and Telegram webhooks. We need to add support for Eliza webhooks which involves 2 tasks:

• Create a "standard/implementation" of Eliza webhooks e.g. 127.0.0.1:8080/eliza/[common-user-id]
  • This URL format should be auto-categorized as Eliza in Webhooks.destination
  • Should auto-select "UserMentioned" event
  • Should only allow the webhook to be created if the [common-user-id] has joined the community i.e. the bot user account has joined the community.
• Add ability to emit UserMentioned event Webhooks for Eliza only
• Modify UserMentioned Knock handler to emit to Eliza webhooks when Eliza user is mentioned
• Add content_url to Webhook data
• Modify Knock workflow to handle UserMentioned

Additional context