Install a github action to run Lighthouse on PR

## I want to do this:

Install a github action to run Lighthouse on PR
These are the coursework repos: https://github.com/CodeYourFuture/Table-of-Contents
These are the template repos: https://github.com/CodeYourFuture/CYF-Coursework-Template

_Given a coursework repo_
When a trainee opens a pull request
And the coursework contains or produces complete HTML pages
Then Lighthouse is run
And the score is reported on the pull request

When the score is less than 100 on Accessibility
Then the PR is set to draft

## Here’s why I want to do it:

We have found that Lighthouse is really helpful for helping trainees evaluate their own code
Setting a lighthouse report on PR is useful for trainees and volunteers to check basic front end quality

## Here’s how it serves our goals:
- automation frees up volunteers for meaningful technical mentorship
- we want trainees to write good code and this will help them and help them see how to fix things
- Also listed on Syllabus https://github.com/CodeYourFuture/syllabus/issues/529

## This is how much time I can put towards this change:
- I can spend 3 hours over 4 weeks testing this for a devops person and merging it in to relevant repos, but I cannot teach someone to do this and then test it for them -- I need devops people to take this forward as I don't have capacity

## This is the help I need from others to get this done (if any):

- a devops grad or volunteer to put this in place
- @Dedekind561 to keep an eye on how it will work with his github actions

Empieza revisando los repositorios de coursework Table-of-Contents y CYF-Coursework-Template, junto con sus workflows existentes de GitHub Actions. Determina cómo puede ejecutarse Lighthouse en pull requests e informar de su puntuación y, a continuación, verifica que el umbral de accesibilidad haga que el PR se convierta en un borrador. Se considerará completado cuando el workflow funcione para los repositorios de coursework y sea compatible con la configuración existente de GitHub Actions.

Escrito por el modelo de indexación a partir del texto del issue.