Enable PVA support in OPIs & add basic data streaming OPI

[Tom-Willemsen]

Description of work

Enable PVA support in OPIs & add an initial, basic, datastreaming OPI.

Ticket

ISISComputingGroup/DataStreaming#26

Acceptance criteria

• An OPI with a pva:// pv in it works.
• Data streaming OPI works

---

Code Review

• Is the code of an acceptable quality?
• If the change is to an OPI, does the check_opi_format.py script in C:\Instrument\Dev\ibex_gui\base\uk.ac.stfc.isis.ibex.opis pass?
• Do the changes function as described and is it robust?
• Is there associated PR for the release notes?

Final Steps

• Reviewer has also merged the release notes