add analytics to docs

[OriolAbril]

Adds google analytics to the documentation page. We'll then gather some data now and after season of
docs we'll be able to see if there is an increase in traffic and retention of visitors.

[sethaxen]

LGTM, once the formatter workflow passes

[OriolAbril]

I added the tracking code to the python website and it doesn't seem to be working, not sure if I generated the wrong codes or there is a bug in the sphinx theme. Somehow we have superfancy analytics for aeviz and everything is different from my personal account and the pymc3 one

Let's see how it goes here

[OriolAbril]

Looks like we'll have the same issue here. I'll try to send a PR to update https://github.com/JuliaDocs/Documenter.jl/blob/master/src/Writers/HTMLWriter.jl#L891 and work with either G- or UA- codes.

[OriolAbril]

It looks like there is an error with the netcdf roundtrip and with summarystats. Are these tests on master or latest version?

[sethaxen]

Looks like we'll have the same issue here. I'll try to send a PR to update https://github.com/JuliaDocs/Documenter.jl/blob/master/src/Writers/HTMLWriter.jl#L891 and work with either G- or UA- codes.

Is JuliaDocs/Documenter.jl#1559 relevant?

It looks like there is an error with the netcdf roundtrip and with summarystats. Are these tests on master or latest version?

These are in the Futures workflow, which is allowed to fail and just lets us know of future breaking changes (from unreleased Jula or ArviZ versions). They shouldn't hold up this PR. The netcdf one I haven't seen before and will look into.

[sethaxen]

The docs build is timing out after 6 hours though. In the past, this has happened due to some mutual incompatibility of some dependency(s) of Soss, Turing, and Documenter, and I've never been able to diagnose it; it usually gets resolved when some version is released.

Pretty much the only way around this besides waiting for it to be fixed elsewhere is probably to split the Quickstart into different pages for Soss, Turing, and CmdStan and execute the examples in their own environment.

[OriolAbril]

Is JuliaDocs/Documenter.jl#1559 relevant?

Indeed, this will fix the issue :). Feel free to merge whenever is best for you, analytics won't work until that PR is merged but in the meantime, this should not break docs nor have any noticeable effect in them, it's only a cryptic javascript error that you can only see if you open the web developer tools.