Add mssql db check before starting tests

[aneesh-joseph]

Add MSSQL DB check before stating the tests

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[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest master at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[mik-laj]

We should add this check also to the docker-compose file. entrypoint.sh is an extra sanity check only.
See:
#13446

In 'scripts/ci/docker-compose/backend-mssql.yml', we should update the depends_on section as follow:

   airflow:
    depends_on:
      mssql:
        condition: service_healthy

See example:
'scripts/ci/docker-compose/backend-mysql.yml'

Ps. This feature is not documented in docker docs, but it wokrs. See: #15509

[potiuk]

Ps. This feature is not documented in docker docs, but it wokrs. See: #15509

Lovely :)