Configure performance monitoring metrics at CI

Ref. PWA01

NOTE: this feature is from a big development. See PWA discussion at GitHub.

Is your feature request related to a problem? Please describe.

By making changes in performance with servers or local machines we’re at risk that things change in the future and that we can’t know for sure when/what/why have changed.

Describe the solution you’d like

To have performance tests, and to control the environment where these tests are executed so it’s always the same (the CI).

For PWA, Lighthouse is the de-facto official tool to check most of the metrics. There are some GH Actions that already do these checks, although if we have other options we’re open to change this for a better solution, for instance, something integrated with RSpec.

https://github.com/marketplace/actions/lighthouse-ci-action
https://github.com/marketplace/actions/lighthouse-check

Additional context

As mentioned in the EPIC:

Lighthouse relevant section

Lighthouse relevant section

As some of these changes could be particular for a given provider (ie it’s not the same Heroku/AWS/OVH/Digital Ocean), at the beginning of these developments there should be done Performance and reproducible testing, and it should also be on someway integrated on the Continuous Integration platform being used at the moment of development so we have a comparison point (an initial picture) and also detect regressions. For instance: https://github.com/marketplace/actions/lighthouse-check

Does this issue could impact on users private data?
No, it’s about performance.

Acceptance criteria

• Given that I’m a Decidim developer
  When I go to the GitHub Actions tab in GH,
  Then I have Lighthouse Workflow sections
  And
  I have the history of this data (at least 90 days).
• Regarding the data I have access to in this Workflow, I can see …
• … First Contentful Paint of the homepage
• … First Contentful Paint of a participatory process
• … First Contentful Paint of a proposal
• … First Contentful Paint of a meeting
• … Speed Index of the homepage
• … Speed Index of a participatory process
• … Speed Index of a proposal
• … Speed Index of a meeting
• … Time to Interactive of the homepage
• … Time to Interactive of a participatory process
• … Time to Interactive of a proposal
• … Time to Interactive of a meeting
• … Largest Contentful Paint of the homepage
• … Largest Contentful Paint of a participatory process
• … Largest Contentful Paint of a proposal
• … Largest Contentful Paint of a meeting