Add per-call request builder

[davidmoten]

Breaking change which allows every api call to

• have custom timeouts
• have extra headers (especially useful for Accept headers to indicate response preference)

This PR

• halves the number of generated client methods (fullResponse now available through the RequestBuilder)
• reduces the size of every generated client method by 6 lines via reuse of a generated private method

[codecov[bot]]

Codecov Report

Attention: 50 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
...oa3/codegen/generator/writer/ClientCodeWriter.java	98.30% <100.00%> (+1.47%)	:arrow_up:
...n/http/service/internal/DefaultHttpConnection.java	87.09% <100.00%> (+1.91%)	:arrow_up:
...rvice/internal/ApacheHttpClientHttpConnection.java	0.00% <0.00%> (ø)
...ain/java/org/davidmoten/oa3/codegen/http/Http.java	44.65% <18.75%> (-6.50%)	:arrow_down:

... and 1 file with indirect coverage changes

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