feat: add flow limiter read interface

[baojinri]

Which issue does this PR close?

Closes #193

Rationale for this change

in order to know flow limiter info when server is running

What changes are included in this PR?

add api to read flow limiter info

Are there any user-facing changes?

none

How does this change test

Existing tests

[codecov]

Codecov Report

Merging #197 (73be8b2) into main (7f1354e) will increase coverage by 20.73%.
The diff coverage is 56.44%.

@@             Coverage Diff             @@
##             main     #197       +/-   ##
===========================================
+ Coverage   39.66%   60.39%   +20.73%     
===========================================
  Files          34       41        +7     
  Lines        4213     4924      +711     
===========================================
+ Hits         1671     2974     +1303     
+ Misses       2317     1570      -747     
- Partials      225      380      +155     

Impacted Files	Coverage Δ
pkg/coderr/code.go	0.00% <ø> (ø)
server/cluster/metadata/types.go	0.00% <0.00%> (ø)
server/coordinator/procedure/util.go	0.00% <ø> (ø)
server/storage/meta.go	0.00% <ø> (ø)
server/storage/storage_impl.go	57.21% <0.00%> (-5.10%)	⬇️
server/member/watch_leader.go	40.62% <20.00%> (-2.71%)	⬇️
server/cluster/manager.go	39.02% <23.07%> (ø)
server/member/member.go	47.39% <45.00%> (-1.32%)	⬇️
server/coordinator/scheduler/scheduler_manager.go	53.96% <47.36%> (ø)
server/coordinator/procedure/manager_impl.go	73.68% <55.55%> (+73.68%)	⬆️
... and 13 more

... and 3 files with indirect coverage changes

[ZuLiangWang]

LGTM