[#268] Add scheduled docker image tests

Description

Problem: Currently we test morley.sh and the docker image based on updated code on each commit in MR. However, we also have stable images in the container registry that needs to be tested.

Solution: Add test-shell-script to the scheduled steps, and use the latest or production image versions depending on the target branch.

TODO: change target branch here and add one more scheduled pipeline for production branch

Related issue(s)

Resolves #268 (closed)

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