fix: parse for the CipherType of Shadowsocks in simplified config

[AkinoKaede]

Because UnmarshalJSONPB method is not used for parse enum, I add a wrapper meassage for workaround.
Alternative names added for consistency with previous.

[codecov-commenter]

Codecov Report

Patch coverage: 3.84% and project coverage change: -0.04 ⚠️

Comparison is base (62bef88) 39.05% compared to head (eda30b2) 39.02%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2510      +/-   ##
==========================================
- Coverage   39.05%   39.02%   -0.04%     
==========================================
  Files         617      618       +1     
  Lines       37036    37071      +35     
==========================================
  Hits        14466    14466              
- Misses      20978    21013      +35     
  Partials     1592     1592              

Impacted Files	Coverage Δ
proxy/shadowsocks/simplified/config.go	2.56% <0.00%> (-0.57%)	⬇️
proxy/shadowsocks/simplified/errors.generated.go	0.00% <0.00%> (ø)
proxy/shadowsocks/simplified/config.pb.go	12.90% <2.63%> (-3.50%)	⬇️
proxy/shadowsocks/config.go	70.89% <33.33%> (+3.51%)	⬆️

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