IRC - code duplication to be consolidated

We will now have IRC information listed in two places:

* [./community/irc.md](https://github.com/JupiterBroadcasting/jupiterbroadcasting.com/blob/main/content/community/irc.md)
* https://jb-live.jupiterbroadcasting.net/ - [./config.jblive.toml](https://github.com/JupiterBroadcasting/jupiterbroadcasting.com/blob/main/config.jblive.toml)

I wonder if we could also consider the Hugo principle of "everything only exists once" ?

_Originally posted by @reclaimingmytime in [#253](https://github.com/JupiterBroadcasting/jupiterbroadcasting.com/issues/253#issuecomment-1209623411_):
> @gerbrent Good point! I agree a general goal is to avoid code duplication, in this case, using Hugo variables for the IRC server, channel and default username and extracting the "prefer your own IRC client?" box to a partial. If the server address changes, it only has to be modified once.
>
> Maybe this can be part of JB 2.0.