publish release notes for v1.12.0-beta.0

[zhzhuang-zju]

What type of PR is this?
/kind documentation

What this PR does / why we need it:
According to the release roadmap, Karmada is about to release v1.12.0-beta.0. This PR is for releasing its release notes.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.25%. Comparing base (9c0bd72) to head (70b5c80).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5762      +/-   ##
==========================================
- Coverage   42.25%   42.25%   -0.01%     
==========================================
  Files         655      655              
  Lines       55756    55756              
==========================================
- Hits        23561    23559       -2     
- Misses      30683    30684       +1     
- Partials     1512     1513       +1     

Flag	Coverage Δ
unittests	42.25% <ø> (-0.01%)	⬇️

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[zhzhuang-zju]

/assign @RainbowMango

[RainbowMango]

/lgtm
/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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• docs/CHANGELOG/OWNERS [RainbowMango]

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