Automatically take nearest next CTF in edge cases

[lucidBrot]

Currently the bot chooses the active CTF based on these steps:

1. If a ctf id was manually specified in the command, use that one.
2. Else if a ctf id is specified in the pinned message of the channel the command was executed in, use that one.
3. Else if a ctf is currently ongoing, use that one
4. Else skip the ctfnote part in channel creation and complain.

In cases where the infrateam is collaborating in advance of the CTF start, or when the ctf time is set wrong, this could be made more convenient by adding a step 3.1 : If no ctf is currently ongoing but there is a unique next CTF that is not further away than N days (or weeks), use that one.

The value of N is TBD. Probably smth like 2 weeks should be fine.

Reason for not going further in time than that limit is that in those cases someone probably simply forgot to import the ctf that was meant. Better use no ctf than a wrong one. Then the user can use the fixup command.

Not urgent.