Deprecation: outbound webhooks

As you may be aware, we recently removed the Stackbit integration from DEV.

One feature we added to support this integration were webhooks with the following three event types:

• article created
• article updated
• article destroyed

However, without the Stackbit integration these hooks don't serve much of a purpose in our current codebase and they have extremely low usage: fewer than 0.005% of users have a non-Stackbit webhook configured.

This means we are deprecating this feature for now (draft PR) and will revisit the topic when we more comprehensively tackle Forem as a platform.