Ext Wortfreunde

Create a TYPO3 extension connector using PHP that receives blog posts from an external source, specifically from [wortfreunde.ch], via webhooks. The system needs to process incoming POST requests at a defined webhook endpoint. It must verify the request signature using an HMAC-SHA256 secret and filter events based on allowed channel IDs. When processing events like `post.published`, it should create or update a `tt_content` element on a configured target page, mapping fields like the post title to `header` and the body to `bodytext` (after converting Markdown to HTML). The configuration should allow setting the webhook secret, allowed channels, and default content type.