Ftr: Add an "api way" to set general configure

[LaurenceLiZhixin]

What this PR does:
This pr add an "API way" to set general configure.
Usage can be found at my branch:
https://github.com/LaurenceLiZhixin/dubbo-go-samples/blob/ftr/samples-add/config-api/go-client/cmd/client.go
or in test file

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-io]

Codecov Report

Merging #1020 (8354e91) into develop (c8fb3e9) will increase coverage by 0.20%.
The diff coverage is 68.84%.

@@             Coverage Diff             @@
##           develop    #1020      +/-   ##
===========================================
+ Coverage    59.54%   59.74%   +0.20%     
===========================================
  Files          261      262       +1     
  Lines        12957    13152     +195     
===========================================
+ Hits          7715     7858     +143     
- Misses        4266     4316      +50     
- Partials       976      978       +2     

Impacted Files	Coverage Δ
common/extension/metadata_service.go	0.00% <0.00%> (ø)
filter/filter_impl/sentinel_filter.go	63.04% <ø> (ø)
metadata/service/remote/service.go	32.95% <0.00%> (ø)
...try/servicediscovery/service_discovery_registry.go	11.56% <ø> (-0.21%)	⬇️
config_center/file/impl.go	50.42% <42.85%> (+0.02%)	⬆️
registry/nacos/registry.go	50.36% <57.14%> (-0.77%)	⬇️
config/config_api.go	74.25% <74.25%> (ø)
registry/etcdv3/registry.go	64.15% <75.00%> (-0.77%)	⬇️
...rotocol/protocolwrapper/protocol_filter_wrapper.go	50.00% <100.00%> (ø)
registry/etcdv3/listener.go	67.50% <100.00%> (+1.71%)	⬆️
... and 16 more

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[AlexStocks]

// enough

[zouyx]

Base on security, I am not agree with modify configuration by web API .

[AlexStocks]

pls change the target branch to 1.5

[gaoxinge]

This pull request may correspond to the dubbo java's api configuration. I think this is a nice configuration feature for people who start to use dubbo-go. @AlexStocks @zouyx

[zouyx]

This pull request may correspond to the dubbo java's api configuration. I think this is a nice configuration feature for people who start to use dubbo-go. @AlexStocks @zouyx

I will agree,if not web API .

[AlexStocks]

very good pr. however, u should add comment for every func.