feat: improve concurrent workers parameter for yurtappset controller

[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:

By adding new startup parameter concurrent-yurtappset-worker for yurtappset controller

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 56.24%. Comparing base (3713163) to head (478c693).
Report is 8 commits behind head on master.

Files	Patch %	Lines
...r/controller/yurtappset/yurt_app_set_controller.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2087      +/-   ##
==========================================
+ Coverage   56.09%   56.24%   +0.14%     
==========================================
  Files         186      186              
  Lines       18092    18044      -48     
==========================================
  Hits        10149    10149              
+ Misses       6910     6864      -46     
+ Partials     1033     1031       -2     

Flag	Coverage Δ
unittests	56.24% <0.00%> (+0.14%)	⬆️

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[zyjhtangtang]

LGTM