chore(zap): support custom fields for zap

[appleboy]

fix #22

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (master@30de6b1). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #45   +/-   ##
=========================================
  Coverage          ?   41.17%           
=========================================
  Files             ?        1           
  Lines             ?       85           
  Branches          ?        0           
=========================================
  Hits              ?       35           
  Misses            ?       47           
  Partials          ?        3           

Flag	Coverage Δ
go-	41.17% <0.00%> (?)
go-1.16	41.17% <0.00%> (?)
go-1.17	41.17% <0.00%> (?)
go-1.18	41.17% <0.00%> (?)
go-1.19	41.17% <0.00%> (?)
macos-latest	41.17% <0.00%> (?)
ubuntu-latest	41.17% <0.00%> (?)

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