[DOP-15023] Improve docker images

[dolfinus]

Change Summary

• Instead of copying the entire repo with all the configs into worker image, copy just syncmaster folder contents.
• Add entrypoint for backend image. It runs migrations first, and only after that it starts an application.
• Add entrypoint for worker image. It starts celery worker with few fixed args, and then applies user-defined args.
• Add syncmaster.backend python module which passes application factory to uvicorn, and then applies user-defined args. This is to keep Horizon and SyncMaster scripts in sync.
• Add syncmaster.db.migrations python module which passes migrations config location to alembic, and then applies user-defined args. This is to keep Horizon and SyncMaster scripts in sync.
• Add healthchecks to docker containers (excluding Oracle).
• Few small cosmetic changes.

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

Attention: Patch coverage is 95.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 91.73%. Comparing base (b7f4d02) to head (a6537e0).

Files	Patch %	Lines
syncmaster/backend/__init__.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #35      +/-   ##
===========================================
- Coverage    91.73%   91.73%   -0.01%     
===========================================
  Files           84       84              
  Lines         2444     2443       -1     
  Branches       305      305              
===========================================
- Hits          2242     2241       -1     
  Misses         145      145              
  Partials        57       57              

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