PEARL: add logic for nominal pressure time calculation in pressure cell controller to IOC and OPI

[rerpha]

Follows on from #6040

As an instrument scientist I would like my IBEX IOC for the pearl pressure controller to tell me what the estimated time is that my pressure cell which reach nominal pressure. Currently there is some logic in the VI which does this:

(target_pressure - current_pressure)/(current application rate/60)

the logic for this should be done in the IOC so a block can be placed on the estimated time if required.

[rerpha]

Closing, this is already in the IOC and OPI, we tested it on WISH during #6762