Add happi/desc fields for future PMPS GUI update

[ZLLentz]

• :HAPPI pv linked to .HappiName could be used to open a relevant typhos ui straight from the diagnostic. This could be included both for FFOs and for the PVs we see in the pre-emptive request screen.
• :DESC pv linked somewhere for the pre-emptive request screen.

I intended to add these myself today but it's a bit late so I'm at least writing them down