chore: update the Dockerfile & docs

[yohamta]

• chore: Updated the Dockerfile to set default DAGU_TZ
• docs: Updated the examples of docker-compose.yaml and Dockerfile

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.97%. Comparing base (4bbcc71) to head (0621a6d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #699   +/-   ##
=======================================
  Coverage   61.97%   61.97%           
=======================================
  Files          53       53           
  Lines        5228     5228           
=======================================
  Hits         3240     3240           
  Misses       1734     1734           
  Partials      254      254           

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