Update VISSR version

[slawr]

CDSP last updated the VISSR version it uses several months ago, whilst the upstream project has continued to evolve. We should look to update to the latest version.

High level task outline:

• Decide VISSR version and create summary of likely code impact (required changes)
• Update submodule and version used in docker
• Sanity test VISSR operation, including with IoTDB
• Update CDSP documentation where necessary

Input notes:

1. @UlfBj has provided the following helpful note about a change in behavior:

I saw the following in your text
You can query what VSS nodes the server understands by asking for the VSS path list using the URL http://localhost:8081/vsspathlist. Entering that URL in your web browser will typically give you a graphical rendering of the JSON data returned.
This is true for VISSRv2.0 (on the v2.0 branch) but not for VISSRv3.0 (on master branch) where I had to diable it due to the new multitree support (it could be restored).

[slawr]

@UlfBj has helpfully pointed out that VISSR now has a hello-world example here https://covesa.github.io/vissr/build-system/hello-world/. We should point to it in CDSP examples list in the documentation site. I mention it here as we should first check whether it needs VISSRv3, i.e. whether we need to do this update first.