Keithley 2290-5 HV power supply

As an electronics technician, I would like IBEX to support a keithley 2290-5 HV power supply.

We already support a keithley 2290-10 - which has a _serial_ interface. However, the keithley 2290-5 does *not* have a serial interface, it only has a GPIB interface. I believe the command set will actually be the same, i.e. we can likely use the same IOC with a macro option to choose whether to connect over GPIB or serial.

Need to discuss whether we have enough GPIB/ethernet converter boxes etc.

### Acceptance criteria
- [ ] We know we can physically connect to a keithley 2290-5 over it's GPIB interface (i.e. we have enough GPIB converters for this etc)
* [ ] Relevant connection details are listed on the wiki
- [ ] Modify the existing `KHLY2290` ioc to allow either serial or GPIB connections
- [ ] Test the existing `KHLY2290` ioc against a `2290-5` communicating over GPIB
* [ ] If trivial modifications are required, these modifications are made
* [ ] If non-trivial modifications are required, new ticket created for them

### Notes

Contact: Max Williams

Note about likely use from MW as of 15/2/2023:

> It will definitely be used but until it is ready we obviously cannot advertise it for use. But with that in mind feel free to have the supply and it can be a background project for yourselves – do appreciate it is more work.