feat: add informer-manager and federated-informer-manager readyz checks

[z1cheng]

Add informer-manager and federated-informer-manager readyz checks

close #272

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (e653c57) 28.63% compared to head (56372f9) 28.63%. Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #277   +/-   ##
=======================================
  Coverage   28.63%   28.63%           
=======================================
  Files         114      114           
  Lines       13565    13565           
=======================================
  Hits         3885     3885           
  Misses       9296     9296           
  Partials      384      384           

Flag	Coverage Δ
unittests	28.63% <ø> (ø)

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[Poor12]

/lgtm /assign @gary-lgy Pls keep the code rebased. :)

[z1cheng]

@Poor12 Thanks for your review! But @gary-lgy proposed an enhancement, see the comment: https://github.com/kubewharf/kubeadmiral/issues/272#issuecomment-1818152972

I will try to implement the proposal.

/hold