Webhook to import/sync content from GitHub with the db

[fennifith]

Initially, content will only get pulled into the database from the GitHub repo. We'll need to define a webhook that pulls content in whenever the main branch is updated.

See: The push event payload - https://docs.github.com/en/webhooks/webhook-events-and-payloads#push

The endpoint must validate that the event was sent from GitHub using the X-Hub-Signature-256 header - see https://docs.github.com/en/webhooks/using-webhooks/validating-webhook-deliveries

The endpoint must ensure that the push was to the main branch of playfulprogramming/playfulprogramming - if not, ignore the event.

The endpoint should look at commits[].added to determine any files that were changed in the push, and dispatch the following tasks:

• Task: Sync author data #31
• Task: Sync collection data #32
• Task: Sync post data #33

[fennifith]

Blocked by #18