stress-test PVWS

[rerpha]

As a developer I would like to see how well PVWS deals with lots of subscriptions. This isn't really likely going to require any code changes in this repository.

we should see how PVWS reacts (pun intended) to:

• subscribing to absolutely every single PV around isis
• subscribing to the same PV 10000 times over different websockets - does it create a monitor for each?
• subscribing to a large number (lets say 10M) of PVs that don't exist

[rerpha]

Given that:

• PVWS makes one connection per PV, rather than per websocket
• the CA gateway will likely be the bottleneck if there is one
• we probably have less PVs than the ORNL usage

I am going to close this ticket as I believe it's superfluous.