In ".gitlab-ci.yml", use "when: manual" for ".template_scenario_files" and ".template_seed_test" to make build pipeline more robust.

In ".gitlab-ci.yml", added documentation and commented out "script" section in ".gitlab/ci/templates/deploy_stage_templates.yml".

In ".gitlab-ci.yml" and ".gitlab-ci-templates.yml", use "${...}" notation to expand variables instead of "$...".

Furthermore, added "manual" trigger to job template ".template_deploy_branch".