add pendantic file

[Ashutosh Singh]

Feature: To pass the project through static analysis

Expected Behaviour: On running dart analyze it should give warnings or errors after pedantic integration is done

Ref: https://pub.dev/packages/pedantic#stricter-than-effective-dart

[Ashutosh Singh]

Also, please resolve all the issues after integrating this in project.

[Sumit Didhate]

@hiashutoshsingh I would like to work on this issue, I am a GSSoC21' participant