Retransmit CTS info messages

[PopFlamingo]

The bot could optionally post CTS information messages (SIRI's general-message endpoint) to a selected Discord room. This way students can be informed of live events occurring on the lanes around the university.

[PopFlamingo]

Here are some mandatory constraints to respect before shipping this feature:

• Make CTS API response parsing more resilient than usual to missing fields: if a field is missing but some useful information can still be delivered to users, make sure to do so.
• Add retry strategies for when a message couldn't be delivered: this includes trying to send the message again (maybe at increasing time intervals, for instance starting at 15s, then 1 minute, then 10 minutes etc...) but also includes longer term retry strategies across bot/system reboots, this has two main advantages:
  • If a reboot occurs at the wrong moment, message retries won't be lost
  • If a message couldn't be delivered due to some bot-side bug, the message can still be delivered once the bug is fixed
• As a direct result of the previous constraint, it is necessary to keep track (in the database) of which messages were/weren't delivered to which user or guild.
• Log all failures to a dedicated file for them to be thoroughly analyzed. This includes all types of failures both on the side of the bot and on the CTS API side.
• Find the most appropriate CTS API fetch interval. This should be respectful of the CTS servers while still providing the most up to date info to users.
• Update the /sources command to indicate when the info messages were last updated and how often they are updated.
• Scan CTS messages in order to attempt detecting urgent messages that should be delivered more prominently (eg: by sending an @everyone, sending a direct message to subscribed users or even reading the message using TTS).