[Don't merge]feature:support HTTP/2 stream push for the Watch API in Server Raft mode

[YvCeung]

• [ ] I have read the CONTRIBUTING.md guidelines.
• [ ] I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov[bot]]

Codecov Report

:x: Patch coverage is 66.66667% with 17 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 69.14%. Comparing base (61e375f) to head (6d37bb5). :warning: Report is 15 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
.../server/cluster/manager/ClusterWatcherManager.java	66.66%	7 Missing and 10 partials :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #7790      +/-   ##
============================================
+ Coverage     66.17%   69.14%   +2.97%     
+ Complexity      994      992       -2     
============================================
  Files          1323     1322       -1     
  Lines         50155    50211      +56     
  Branches       5928     5943      +15     
============================================
+ Hits          33190    34720    +1530     
+ Misses        14053    12563    -1490     
- Partials       2912     2928      +16     

Files with missing lines	Coverage Δ
.../server/cluster/manager/ClusterWatcherManager.java	73.56% <66.66%> (-0.95%)	:arrow_down:

... and 180 files with indirect coverage changes

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