Lighthouse ci action

[tunetheweb]

Fixes #1178

Adds Automatic Lighthouse checks to our Test Website action to test for regressions as good changes.

Note we disable a few checks:

• Time-based performance checks are disabled as too unreliable
• Optimisations we don't currently perform (e.g. minifying CSS and JS and removing unused CSS and JS)
• Turns off items that don't work on dev server (e.g. Canonical is incorrect, Compression is not used, Crawling is disabled...etc.).

This means we should only get real failures.

I also added a weekly run against production action. This looks at Lighthouse scores - though again not Performance due to variability as really want to avoid introducing noisy checks that create false alerts sometimes.

As well as avoiding #1216 (which is where this whole thing came from!) it's also identified another couple of issues meaning we have less than perfect scores:

• The Spanish CSS chapter has an empty link
• Links with lints don't have enough spacing on mobile

I think this shows the value of automating these checks!

Monitoring performance needs some more thought. We could do several runs to average, and set thresholds, or leverage the Page Speed Insights API to get CrUX data or something similar. Anyway think this PR has enough value even without explicit performance monitoring.

Interested to hear your thoughts!

[rviscomi]

Thanks @bazzadp for the PR. Excited about LH integration. I'll defer to @ibnesayeed's review.

[ibnesayeed]

I am okay with the other changes except the last one where I think using jq for building and formatting the config file would be better than manually doing it, which is brittle as it introduces tight coupling between the config file format and the shell script.

[ibnesayeed]

LGTM!

However, I wish there was a way in lighthouse to supply list of URIs separately, without mixing it into the config file. Please see if there are any configuration options that can point to a file for list of URIs. That said, this PR can be merged, and if a better approach is found, we can make necessary changes later.