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

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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

[rerpha]

is this intended to be committed on this PR/is it an artifact of a branch that is yet to be rebased?

[rerpha]

actually sorry im being stupid - it's PVA support isn't it? how do we set EPICS_CA_ADDR_LIST though normally?

[Tom-Willemsen]

Yes, this is PVA support.

We set epics CA address lists via a .properties file, but as far as I could tell no such properties exist for PVA and env/system variables were the only way to configure this for PVA.

I also found the PVA support in CS-Studio a bit flaky especially on reconnection - would be curious if you find the same. If so it's probably something we need to look into...

[rerpha]

have created ISISComputingGroup/DataStreaming#43 to look into the weird pva disconnect issue but this looks a good start.

[rerpha]

although could you add the dummy widget pls @Tom-Willemsen