Add ability to fetch number of tests a scenario would run

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR adds ability to fetch no of examples a scenario would run without actually running the examples. This will be later used to eliminate jobs with zero examples by creating dynamic child pipelines if a scenario has one or more examples.

Required for: https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/564

How to set up and validate locally

From the qa directory, run:

bundle exec bin/qa Test::Instance::Smoke http://gdk.test:3000 --count-examples-only

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.