fix(#259): docker-compose error on building sample project.

[NaGaii1994]

• Change base image from alpine to slim-bullseye because using alpine can make python docker slower.
• Update postgres image from 9.6 to 14.
• Fix bug that django container connect database before database is ready.

[abhiabhi94]

hey @NaGaii1994 thanks for taking the time to contribute. left some comments, rest of the patch looks fine to me.

[codecov-commenter]

Codecov Report

Base: 99.89% // Head: 99.89% // No change to project coverage 👍

Coverage data is based on head (02ee66a) compared to base (0d600b9).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #260   +/-   ##
========================================
  Coverage    99.89%   99.89%           
========================================
  Files           56       56           
  Lines         1994     1994           
  Branches       162      161    -1     
========================================
  Hits          1992     1992           
  Misses           1        1           
  Partials         1        1           

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