fix: write default app config on app init

[sandeep-paliwal]

Always create .aio file with default app config for app init command.
Fixes #355

Description

When aio app is initialised with -y flag, .aio file was not created.
Fixed this by writing .aio file with default app config at app init. When import or CLI login is used, .aio file will be merged with project config.
Default app config includes, name of actions, dist and web-src folder. This will help users to customise app if required.

Related Issue

Motivation and Context

How Has This Been Tested?

unit tests, manual app init test

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #353 (64b77c0) into master (3dab508) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #353   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         1331      1335    +4     
  Branches       219       219           
=========================================
+ Hits          1331      1335    +4     

Impacted Files	Coverage Δ
src/commands/app/init.js	100.00% <100.00%> (ø)
src/lib/import.js	100.00% <100.00%> (ø)

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