INTER: show logic state in IBEX GUI, forward plc axis description to .DESC

[rerpha]

As an INTER scientist I would like to see:

• A description of an axis which matches what the PLC says in the table of motors
• the logic state that the INTER beckhoff is in
• the logic state that the INTER beckhoff last errored in

Acceptance criteria

• Above fields are populated and shown in IBEX

[rerpha]

closes #6860

[rerpha]

ISISComputingGroup/EPICS-motorExtensions#57
ISISComputingGroup/EPICS-ioc#808
ISISComputingGroup/ibex_gui#1595
#7992

note added to https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/Beckhoff-commissioning#fields-that-arent-automatically-populated

patched onto NDXINTER - to review see the PVs changed working on there (point your client at NDXINTER)

[rerpha]

child of #7532

[rerpha]

This is now patched on NDXINTER, so can VNC in to see the OPI, however the beckhoff will be on and off for the next few days while we're commissioning. Will update this comment with a screenshot or something for the reviewer to confirm that DESC forwarding is working fine

[KathrynBaker]

As per a discussion relating to the difficulties in reviewing it, progressing it as completed