Use Pa11y 7, require Node 18, fix issues

[danyalaytekin]

This PR updates the service to use pa11y@7, updates the minimum version of Node.js required to 18, and makes several other changes to modernise the project.

Changes

• Dependencies
  • Raise minimum Node.js requirement to 18 from 12
  • Use pa11y@7 in place of 6
  • Use hapi@21 in place of 20
  • Use actions@setup-node@4 in place of 3
  • Remove request
• Code
  • Restore CI build's Ubuntu environment to ubuntu-latest from ubuntu-20.04
  • Allow ES2020 syntax, and use it in some places to reduce repetition & tighten signatures
  • Replace remaining use of make with npm scripts
  • Use util.promisify to flatten some async code
  • Replace use of request with fetch throughout
  • Rename some ambiguous use of env to mode for clarity
  • Remove some comments where they repeated adjacent code names
  • Rewrite several tests to async syntax, replacing done syntax
  • Tidy up test setup
• Documentation
  • Document an option to use nektos/act to test locally

Changes during review process

• d8d977e Add link to Docker Desktop
• d24182d Add link to nektosact.com and mention other ways to install act
• 0f9b6e0 Be clearer that act is for locally testing GitHub Actions
• d857fb1 Mention installation options across both Docker Desktop and act; use shortlinks for consistency

Thanks for the review and documentation fixes @hollsk

[hollsk]

Superb, thank you so much @danyalaytekin 🙏

There's a few lint warnings in model/task.js. All of them are about complexity though, and i think it's probably more important at this point to just get this merged and worry about decomplexifying those blocks later.

Aside from that, i just added suggestions with direct links to Docker and Act.

[danyalaytekin]

Thanks @hollsk, I've committed those and added one more (added a list at the bottom of the PR description). I don't think the linters' warnings were introduced by this PR, including the nesting one since the previous version had nesting 3 as well, unless the rule doesn't apply to inline functions, but I agree about placating them at some point for the various codebases they're affecting.

[hollsk]

Oh yes, love opening up a codebase and finding ancient lint errors in it 😆 Looks perfect, thank you!