Feat: webhook support for added, edited and deleted bookmarks

[pava0]

Hi everyone! New contributor here!

This PR addresses the feature idea #492 for a simple POST webhook to send the newly added/updated/deleted bookmark to other self-hosted services like crawlers (The Wayback Machine, Browsertrix), notification servers (Gotify, ntfy.sh) or worfklow automation platforms (n8n, Node-Red).

At the moment this feature allow the user to receive in the body of the request the event type ("new_bookmark", "updated_bookmark" or "deleted_bookmark") and the relevant data (url, id, owner username, title, description, notes, website title, website description, date added and tags).
This happens only for the bookmarks that have a user specified tag (e.g. "crawl").

I've also added a simple username:password authentication method for webhooks served behind credentials.

At the moment it's just a simple POST request.
If @sissbruecker thinks it is worth it to expand this feature further, these are possible improvements:

• Choice between POST requests (with bookmark's data in the body) and GET request with data encoded in the URL
• User configurable body content for POST request (select which fields to include and how to name them)
• List based tag-webhook system, to allow different tags to send requests to different webhooks (one for youtube-dl, one for page s to archive, etc)
• Add a button on the view page for the bookmark to manually send the URL to a specific endpoint.

Let me know what you think, and thank you for Linkding! I've been using it regularly for more than a year

[gusvd]

This would be super beneficial for my use-case. Future improvement would be to also send webhooks for deleted and modified entries.

[pava0]

This would be super beneficial for my use-case. Future improvement would be to also send webhooks for deleted and modified entries.

Updated the PR to push the webhook for added, updated or deleted bookmarks.