Cherry pick partition key fix and example

[congqixia]

/kind improvement

[sre-ci-robot]

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[codecov]

Codecov Report

Merging #541 (016e629) into master (8b6a432) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #541      +/-   ##
==========================================
+ Coverage   82.55%   82.59%   +0.04%     
==========================================
  Files          39       39              
  Lines        3542     3540       -2     
==========================================
  Hits         2924     2924              
+ Misses        505      504       -1     
+ Partials      113      112       -1     

Files Changed	Coverage Δ
client/insert.go	79.16% <ø> (+0.54%)	⬆️

[yah01]

/lgtm