Prevent video chat link scraping

[ghost]

We tend to post zoom links in our chat descriptions which are publicly available. This means that a scraper can intercept our zoom links and appear in our chats and interrupt them.

It would be nice to remove zoom links from descriptions anyway because they are only useful before the meeting. The description should just be text that describes the chat.

We need to agree upon a solution before we get started with this. Idea: add a new meeting_link field to the PennyChatInvitation model (not the PennyChat model), and make a separate field in the chat modal to account for this. There are 2 problems though: 1) the modal already takes up too much space on the screen 2) there might be other similar fields that we eventually want (like notes_link).