Put Xiao Zhang to the maintainer list

[RainbowMango]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

This PR adds Xiao Zhang(@wawa0210) to the maintainer list as per the vote result at karmada-io/community#55.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3482ee8) 51.91% compared to head (c79beb2) 51.90%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4392      +/-   ##
==========================================
- Coverage   51.91%   51.90%   -0.02%     
==========================================
  Files         243      243              
  Lines       24146    24146              
==========================================
- Hits        12536    12533       -3     
- Misses      10928    10930       +2     
- Partials      682      683       +1     

Flag	Coverage Δ
unittests	51.90% <ø> (-0.02%)	⬇️

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[XiShanYongYe-Chang]

Good~
/lgtm

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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