⏳ Handle expiring messages

[nickvergessen]

Server ref https://github.com/nextcloud/spreed/issues/7359

Tasks:

• [ ] Make sure items are removed from the view when their message expiration is reached even when the user doesn't leave the conversation
• [ ] Make sure when entering a conversation we don't show messages that expired in the meantime
• [x] Handle system message

Follow-up possible:

• [ ] Add an option to set the expiration with:
  • Off
  • 4 weeks
  • 1 week
  • 1 day
  • 8 hours
  • 1 hour