Upgrade Halo runtime environment to JRE 21

[JohnNiang]

What type of PR is this?

/kind improvement
/area core
/milestone 2.13.x

What this PR does / why we need it:

Last month, Eclipse has released OpenJ9 0.42 supported Java 21. It's time for Halo to run JRE 21.

Closes #4929

Does this PR introduce a user-facing change?

升级 Docker 镜像的运行环境至 JRE 21。

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.3% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2cf19a4) 56.91% compared to head (5fdf6c0) 56.91%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5341   +/-   ##
=========================================
  Coverage     56.91%   56.91%           
  Complexity     3319     3319           
=========================================
  Files           587      587           
  Lines         18968    18968           
  Branches       1401     1401           
=========================================
  Hits          10795    10795           
  Misses         7594     7594           
  Partials        579      579           

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[JohnNiang]

/ping @halo-dev/sig-halo

[ruibaby]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: guqing, ruibaby

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