probe-desktop: add full support for using OONI Run v2 links

[hellais]

This issue is the probe-desktop issue about implementing the UI part which takes in an OONI Run link descriptor and renders the appropriate test card in the dashboard view. See: "3.0 OONI Run descriptor": https://github.com/ooni/spec/blob/master/backends/bk-005-ooni-run-v2.md#30-ooni-run-descriptor.

Since on desktop we don't currently have any OONI Run link support, we can probably defer to doing this at a later stage and do it all in one go, by also adding fully support for scheduling tests and running the links.

xref: #2471

[hellais]

We should discuss with @bassosimone and @majakomel if there is anything missing from the engine to support this in desktop.

[jbonisteel]

Out of scope for Mozilla grant.

[jbonisteel]

Given expanded timeline, I wonder if we want to consider adding this in? Sometimes to discuss during the next roadmap meeting.