Add ability to install gitlab-qa via Gemfile

What does this MR do?

Adds parametrised before_script block of .gitlab-qa-install to run bundle install instead of gem install gitlab-qa when RUN_WITH_BUNDLE environment variable is set. This allows to reuse same templates in projects which control gitlab-qa version via Gemfile.

Check-list

• Verify the change in all affected pipelines.

• gitlab run: https://gitlab.com/gitlab-org/gitlab/-/pipelines/625773955

• staging run: https://ops.gitlab.net/gitlab-org/quality/staging/-/pipelines/1389767