feat(HTL-111103): Enable custom header for drawer component

[coolestKev]

1. Adding a unit test to verify how custom headings behave.
2. Removed redundant string | React.ReactNode type declaration.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.78%. Comparing base (326163c) to head (1175981).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1528      +/-   ##
==========================================
+ Coverage   93.67%   93.78%   +0.11%     
==========================================
  Files         149      149              
  Lines       11284    11284              
  Branches      686      687       +1     
==========================================
+ Hits        10570    10583      +13     
+ Misses        685      677       -8     
+ Partials       29       24       -5     

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