airframe-okhttp: Scala 3 support

[xerial]

• Use the standard HttpMessage.Request/Response types for the library interface airframe-http: Deprecate the legacy HttpClient[F[_], Req, Resp] interface #2440
• Use the same SyncClient code to use the common retry/circuit breaker logic

[codecov]

Codecov Report

Merging #2865 (4d8ccfa) into master (e42aa86) will decrease coverage by 0.04%.
The diff coverage is 82.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2865      +/-   ##
==========================================
- Coverage   82.80%   82.76%   -0.04%     
==========================================
  Files         340      341       +1     
  Lines       14437    14396      -41     
  Branches     2354     2364      +10     
==========================================
- Hits        11954    11915      -39     
+ Misses       2483     2481       -2     

Impacted Files	Coverage Δ
...scala/wvlet/airframe/http/client/HttpChannel.scala	0.00% <0.00%> (ø)
...scala/wvlet/airframe/http/client/HttpClients.scala	78.30% <ø> (ø)
...ain/scala/wvlet/airframe/http/okhttp/package.scala	74.00% <57.14%> (-5.17%)	⬇️
...ala/wvlet/airframe/http/okhttp/OkHttpChannel.scala	89.28% <89.28%> (ø)
...main/scala/wvlet/airframe/http/okhttp/OkHttp.scala	100.00% <100.00%> (ø)
...wvlet/airframe/http/client/JavaClientChannel.scala	95.12% <100.00%> (ø)
...c/main/scala/wvlet/airframe/http/HttpMessage.scala	87.20% <100.00%> (+0.10%)	⬆️

... and 2 files with indirect coverage changes

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[xerial]

@shimamoto @takezoe This is a breaking change to support Scala 3 and reuse the same HTTP client code base as much as possible between various clients (Java9 HTTP client, URLConnectionClient, OkHttp client, etc.) The basic usage will be as described in #2440