Feat/nacos registry

[Mulavar]

What this PR does:
add nacos registry&discovery

Which issue(s) this PR fixes:

Fixes #534

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Patch coverage: 66.66% and project coverage change: +0.37 🎉

Comparison is base (e4b196d) 36.67% compared to head (5ac1480) 37.05%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #659      +/-   ##
==========================================
+ Coverage   36.67%   37.05%   +0.37%     
==========================================
  Files         202      205       +3     
  Lines       22484    22437      -47     
==========================================
+ Hits         8247     8313      +66     
+ Misses      13321    13205     -116     
- Partials      916      919       +3     

Impacted Files	Coverage Δ
pkg/mysql/server.go	0.00% <ø> (ø)
pkg/config/nacos/nacos.go	63.54% <33.33%> (+3.03%)	⬆️
pkg/util/config/nacos.go	75.55% <75.55%> (ø)

... and 33 files with indirect coverage changes

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