Make `script:` optional since containers can already predefine a task to be run via ENTRYPOINT

Problem to solve

We require a script section now in any job, but it's possible when using containers to define an ENTRYPOINT. If your script uses a container that just does one thing, that already has an entrypoint you need to do something like the following or you will get a YAML error:

superlinter:
  image: github/super-linter:latest
  script: [ "true" ]
  variables: { RUN_LOCAL: "true", DEFAULT_WORKSPACE: $CI_BUILDS_DIR }

The script: [ "true" ] part doesn't actually do anything (it's not even run), but it's the only way to not get a parsing failure.

Intended users

User experience goal

Proposal

Make script optional.

Further details

Permissions and Security

Documentation

Availability & Testing

What does success look like, and how can we measure that?

What is the type of buyer?

Is this a cross-stage feature?

Links / references