Fix plausible script tags and make them configurable

[rogermparent]

Before, the plausible scripts added by this theme were:

1. broken in some metrics like bounce rate because the Script tag put them at the bottom.
2. all hard-coded to point to dvc.org 😬

This PR changes that by turning the plausible domain and script source into options configurable via Gatsby's siteMetadata feature under the keys plausibleDomain and plausibleSrc.

• plausibleDomain determines the domain the site reports to Plausible as, and if it isn't specified the domain is inferred from siteMetadata.siteUrl

• plausibleSrc allows us to specify the src tag of the plausible script, defaulting to our websites-server-proxied version of the outbound-links script. Cases where this would be overridden would include:

  • using the non-outbound-links version of the script
  • using a proxy at a path different from websites-server
  • using a non-proxy version

  This will change once we shift toward making this more useful to the public

⚠️ I've rebased this branch onto a new maintenance branch that reverts #33, so we can make a bugfix release on the 0.1 line and make this fix get in ASAP

Here's an example of the resulting script tag

[yathomasi]

Thanks for the catch @rogermparent.

We use websites-server on all our websites. The proxy should be available to all the websites themselves i.e we will not need the dvc.org prefix.
For convenience, we can

1. set the plausibleSrc to /pl/js/script.outbound-links.js or /pl/js/script.js by default,
2. we will also need plausibleAPI which we can set to /pl/api/event by default,
3. for plausibleDomain I think we can extract it from siteUrl metadata. Instead, we can replace plausibleDomain with a flag variable(which is set to true by default) and set it to false in case we don't want to use it(for instance, the gatsby-theme-iterative example website).

This way we have fewer configurations to do on consumer websites and we can replace the variable only when it's necessary.

[rogermparent]

I'm struggling to find out where we actually put /pl/api/event link, I'm looking over all the existing plausible code but it seems like the only two values used are the domain and src that links import from. In the meantime, I'll add the automagic setup for what this PR has to make the patch more seamless.

[rogermparent]

falsiness can be triggered with a plausibleDomain of '', but that API will be improved in the next revision.

[rogermparent]

Found it! It's just data-api on the main script 🤦. Integrating it now.

[rogermparent]

We can get away with a lot of plug-and-play for our websites, but I think we shouldn't have a default show through on siteUrl, especially not cml.dev.

[yathomasi]

We provide siteUrl for individual websites, so we don't need a default value. It will be required field for individual website.

[yathomasi]

Looks good to me. Nice work @rogermparent.

[jorgeorpinel]

Hi. Now that this has been merged everywhere, should we setup some follow-up date to check on the bounce rates?

[rogermparent]

I've actually been checking in the whole time! Bounce rates went down immediately after the initial quickfix, and have stayed at that same low/normal level with all other metrics normal ever since the merge. My last check was Monday, and I planned to give yet another Friday for extra measure.