Implement multiplexer proxy.

[zyjhtangtang]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Implement the shared cache module in node-level traffic multiplexing, referencing the Design Proposal.

Does this PR introduce a user-facing change?

"NONE"

[codecov]

Codecov Report

Attention: Patch coverage is 49.37429% with 445 lines in your changes missing coverage. Please review.

Project coverage is 45.35%. Comparing base (ea999d4) to head (59483aa).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
.../yurthub/proxy/multiplexer/watchembeddedencoder.go	10.66%	130 Missing and 4 partials ⚠️
pkg/yurthub/proxy/multiplexer/multiplexerwatch.go	51.21%	43 Missing and 17 partials ⚠️
pkg/yurthub/multiplexer/storage/fake_storage.go	0.00%	49 Missing ⚠️
pkg/yurthub/proxy/multiplexer/multiplexerlist.go	51.42%	19 Missing and 15 partials ⚠️
pkg/yurthub/proxy/multiplexer/multiplexerproxy.go	72.26%	22 Missing and 11 partials ⚠️
pkg/yurthub/multiplexer/multiplexer.go	75.25%	12 Missing and 12 partials ⚠️
pkg/yurthub/proxy/util/util.go	0.00%	19 Missing ⚠️
pkg/yurthub/proxy/proxy.go	0.00%	14 Missing ⚠️
pkg/yurthub/filter/filterchain/filterchain.go	0.00%	13 Missing ⚠️
pkg/yurthub/filter/manager/manager.go	0.00%	10 Missing ⚠️
... and 12 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2141      +/-   ##
==========================================
+ Coverage   45.29%   45.35%   +0.05%     
==========================================
  Files         406      422      +16     
  Lines       27899    28739     +840     
==========================================
+ Hits        12637    13034     +397     
- Misses      14023    14400     +377     
- Partials     1239     1305      +66     

Flag	Coverage Δ
unittests	45.35% <49.37%> (+0.05%)	⬆️

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate passed

Issues
7 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.6% Duplication on New Code

See analysis details on SonarQube Cloud

[rambohe-ch]

/LGTM