[Improvement] Set a default app id if not provided in the app configuration

[deshraj]

Description

Several folks have mentined this issue that their app data is not persisted when they init the app using app = App().

This is because we were setting a new app id every time someone does an init. We are changing this behavior to set a default app id unless user specifically configures it in their app configuration during init time.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Documentation update

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.85%. Comparing base (7e1d2ff) to head (8f8a0cb).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1300      +/-   ##
==========================================
- Coverage   55.85%   55.85%   -0.01%     
==========================================
  Files         153      153              
  Lines        6171     6170       -1     
==========================================
- Hits         3447     3446       -1     
  Misses       2724     2724              

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