Update docs on running e2e tests locally

What does this MR do and why?

Describe in detail what your merge request does and why.

Update documentation on running e2e tests by using bundle exec rspec in examples instead of custom bin/qa runner.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Closes https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/1034