📖 Update doc to add lease for cluster extension sample

[rashmi43]

Description

fixes: #1478

Reviewer Checklist

• API Go Documentation
• Tests: Unit Tests (and E2E Tests, if appropriate)
• Comprehensive Commit Messages
• Links to related GitHub Issue(s)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.73%. Comparing base (7ffb2ea) to head (8db08a1).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1488      +/-   ##
==========================================
+ Coverage   74.69%   74.73%   +0.03%     
==========================================
  Files          42       42              
  Lines        3241     3241              
==========================================
+ Hits         2421     2422       +1     
+ Misses        647      646       -1     
  Partials      173      173              

Flag	Coverage Δ
e2e	52.32% <ø> (-0.10%)	⬇️
unit	57.20% <ø> (+0.03%)	⬆️

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[tmshort]

/lgtm

[tmshort]

Merging as this is a doc update.