feat(typings): add ClusterOptions['serialization']

[waitingsong]

ref: eggjs/egg-cluster#97

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Merging #4182 into master will not change coverage by %.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #4182   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           34        34           
  Lines          954       954           
=========================================
  Hits           954       954           

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