[Feature Request] Edit information in slack/discord pings and intervals

[ghost]

So currently there is a set message which shows the information, of the fleet. But i would like the ability to add more information.
So for example currently it just shows the start date time, duration, importance and the FC.
In my case, I would also like to add a bit of a description to what the fleet is about without people having to click to login to the website.
Next, there is only currently pings for 1 hour before, 30 minutes then 15minutes. It would be nice if this was customisable in the settings. For example 1 day before, 3 hours etc...

Just a few quality of life suggestions.

[H4Z4RD-H42]

To merge with this: #16

[alkari-verende]

The second half of this request is addressed in #61