Consider doing encore style testing as part of OONI Run links

[hellais]

It would be cool if when a user visits and OONI Run link and they don't have OONI Probe installed, they also start an encore style test and submit measurements to OONI.

Here in an ancient ticket about this:
ooni/probe#471

Relevant research:
https://arxiv.org/pdf/1410.1211.pdf
https://bdes.datasociety.net/wp-content/uploads/2016/10/Encore-Case-Study.pdf

[hellais]

I am adding this to the Experiments project too as it's relevant to that as well.
cc @bassosimone