user can add attachment

[pantianying]

What this PR does:

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 #398 into develop will decrease coverage by 0.05%.
The diff coverage is 25%.

@@            Coverage Diff             @@
##           develop    #398      +/-   ##
==========================================
- Coverage    67.36%   67.3%   -0.06%     
==========================================
  Files          161     161              
  Lines         8331    8335       +4     
==========================================
- Hits          5612    5610       -2     
- Misses        2196    2202       +6     
  Partials       523     523

Impacted Files	Coverage Δ
config/generic_service.go	0% <ø> (ø)	⬆️
common/proxy/proxy.go	93.06% <25%> (-2.81%)	⬇️
config_center/nacos/facade.go	64.7% <0%> (-8.83%)	⬇️
filter/filter_impl/hystrix_filter.go	68.64% <0%> (-3.39%)	⬇️
protocol/dubbo/client.go	69.09% <0%> (+1.21%)	⬆️
cluster/cluster_impl/failback_cluster_invoker.go	80.64% <0%> (+2.15%)	⬆️

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[fangyincheng]

LGTM

[zouyx]

LGTM

[hxmhlt]

LGTM