add Matomo analytics

[egpbos]

Fixes #97.

Changes proposed in this pull request:

• Activate Matomo analytics (using the NLeSC Matomo server). This thankfully is implemented in the elixir-toolkit-theme already, so we only need to add two lines in config.yml!
• Add privacy policy. I was going to copy the one for the EVERSE main site introduced in Matomo website stats EVERSE-ResearchSoftware.github.io#70, but may want to also take some inspiration from the RDMkit one: https://github.com/elixir-europe/rdmkit/blob/master/pages/about/privacy.md?plain=1

Notes for reviewers:

• I did not add the privacy policy yet, so please don't merge yet! I opened the PR to be able to test the build on Netlify.
• Ready for review!

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[egpbos]

The Matomo tag does not show up in the Netlify build. This is because apparently it does not build in Jekyll "production mode". The analytics tags are disabled outside of production mode in ETT. I tested locally, and there it does work.

Will now continue with the privacy policy.

[egpbos]

The following page lists 12 steps to be taken for a cookieless GDPR compliant site: https://matomo.org/faq/new-to-piwik/how-do-i-use-matomo-analytics-without-consent-or-cookie-banner/

I think we only strictly need to do step 1, which is to add a single line of Javascript that disables cookies, and step 12, adding a privacy policy (that can be copied from the main EVERSE site).

In addition, a "recommended" step is to provide a Matomo opt-out button (step 11 in the list). I think the main EVERSE website also tried to do that, but on my browser I cannot actually find it anywhere. @graeme-a-stewart is that expected?

The other steps should be configured in the NLeSC Matomo instance already, because it was setup with GDPR compliance.

[egpbos]

I tried to first do a PR to ETT for the cookie disabling line: ELIXIR-Belgium/elixir-toolkit-theme#314

If that goes through, we have to add in this PR a config.yml line to turn the Matomo cookies off. However, it may be a while before the ETT feature is released, so I will now also add a quick workaround in this PR that we can easily remove later.

[egpbos]

Ready for review! As noted above, Matomo doesn't actually work on Netlify, so you'll have to build on your laptop to test if you like. I also did so, and it is working for me, so you can also trust me on that and see how that works out ;)

[egpbos]

@graeme-a-stewart: I modified the privacy text slightly. Matomo does still create cookies, but the important part is that no personally identifiable info is included in them (see the "Essential blabla" section here: https://matomo.org/faq/general/faq_157). Doesn't really matter much for privacy purposes, I think, but just a minor edit for completeness.