fix(typings): optimize declaration of httpclient

[whxaxes]

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

补充并完善 httpclient 里支持的配置

[codecov]

Codecov Report

Merging #3665 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #3665    +/-   ##
=======================================
  Coverage     100%    100%            
=======================================
  Files          34      34            
  Lines         943    1147   +204     
=======================================
+ Hits          943    1147   +204

Impacted Files	Coverage Δ
lib/egg.js	100% <0%> (ø)	⬆️
app/extend/request.js	100% <0%> (ø)	⬆️
app/extend/response.js	100% <0%> (ø)	⬆️
lib/core/httpclient.js	100% <0%> (ø)	⬆️
config/config.default.js	100% <0%> (ø)	⬆️
lib/loader/app_worker_loader.js	100% <0%> (ø)	⬆️
lib/core/base_context_logger.js	100% <0%> (ø)	⬆️
lib/core/dnscache_httpclient.js	100% <0%> (ø)	⬆️
lib/agent.js	100% <0%> (ø)	⬆️

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[atian25]

2.22.2~~~