fix/updateV4MigrationGuide

[tusharpandey13]

This is a doc change.
Updated links in v4 migration guide to point to main.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.69%. Comparing base (9cccf91) to head (a071ecd).
Report is 18 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1925   +/-   ##
=======================================
  Coverage   74.69%   74.69%           
=======================================
  Files          19       19           
  Lines        1379     1379           
  Branches      210      210           
=======================================
  Hits         1030     1030           
  Misses        342      342           
  Partials        7        7           

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