fix: support cache response for partial object metedata watch request

[rambohe-ch]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage

/kind feature

What this PR does / why we need it:

improve saveWatchObject function in cache manager for supporting paritialobjectmetadata watch requests.

Which issue(s) this PR fixes:

Fixes #2199

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

[codecov]

Codecov Report

Attention: Patch coverage is 73.52941% with 9 lines in your changes missing coverage. Please review.

Project coverage is 45.16%. Comparing base (7763e7c) to head (a4c84bc).
Report is 49 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/yurthub/proxy/util/util.go	50.00%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2209       +/-   ##
===========================================
- Coverage   58.93%   45.16%   -13.78%     
===========================================
  Files         210      402      +192     
  Lines       18968    27781     +8813     
===========================================
+ Hits        11179    12546     +1367     
- Misses       6707    14003     +7296     
- Partials     1082     1232      +150     

Flag	Coverage Δ
unittests	45.16% <73.52%> (-13.78%)	⬇️

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[vie-serendipity]

/LGTM

[vie-serendipity]

openyurt/pkg/yurthub/cachemanager/cache_manager.go

Line 356 in 09078b4

func (cm *cacheManager) saveWatchObject(ctx context.Context, info *apirequest.RequestInfo, r io.ReadCloser, stopCh <-chan struct{}) error {

BTW, I noticed that stopCh parameter is not used in saveWatchObject function. I think this could be optimzed.

[zyjhtangtang]

/LGTM