feat: improve proxy handler of yurthub

[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:

1. remove latency metrics(proxyLatencyCollector) of yurthub, because this metric is not useful for end users.
2. remove WithMaxInFlightLimit handler, because requests are aggregated by multiplexer in yurthub, so requests limit is not needed for controlling requests volume.
3. remove WithCacheHeaderCheck handler, because Edge-Cache header is rarely used.
4. improve WithRequestClientComponent handler, add whole user agent into request context, and truncate user agent by callers.
5. improve proxy handler not to depend on working mode.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

[sonarqubecloud]

Quality Gate failed

Failed conditions
5.9% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 36.58537% with 52 lines in your changes missing coverage. Please review.

Please upload report for BASE (master@ffb736a). Learn more about missing BASE report.
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/yurthub/proxy/util/util.go	3.57%	27 Missing ⚠️
pkg/yurthub/util/util.go	0.00%	10 Missing ⚠️
pkg/yurthub/proxy/remote/loadbalancer.go	0.00%	6 Missing ⚠️
pkg/yurthub/cachemanager/cache_manager.go	83.87%	3 Missing and 2 partials ⚠️
pkg/yurthub/proxy/proxy.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2301   +/-   ##
=========================================
  Coverage          ?   45.51%           
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  Files             ?      408           
  Lines             ?    27049           
  Branches          ?        0           
=========================================
  Hits              ?    12310           
  Misses            ?    13522           
  Partials          ?     1217           

Flag	Coverage Δ
unittests	45.51% <36.58%> (?)

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[rambohe-ch]

@zyjhtangtang @YTGhost PTAL

[zyjhtangtang]

/LGTM