Blind SSRF in `/home/testdiscord` endpoint

Medusa is an automatic video library manager for TV shows. Versions prior to 1.0.19 are vulnerable to unauthenticated blind server-side request forgery (SSRF). The testDiscord request handler in medusa/server/web/home/handler.py does not validate the user-controlled discord_webhook variable and passes it to the notifiers.discord_notifier.test_notify method, then _notify_discord and finally _send_discord_msg method, which sends a POST request to the user-controlled URL on line 64 in /medusa/notifiers/discord.py, which leads to a blind server-side request forgery. This issue allows for crafting POST requests on behalf of the Medusa server. Version 1.0.19 contains a fix for the issue.