Added WithClientRequestName function

[yklyahin]

I have not found a way to change the default function "ClientRequestName" in the middleware for HTTP client.

[axw]

Thanks @lobotomist! Would you mind adding a test please?

[yklyahin]

@axw Sure. I noticed that most of the option functions do not have unit tests.

[axw]

Thanks @lobotomist, looks good. The existing options are tested, just not directly. e.g. WithRecovery is tested by module/apmhttprouter. I'll add more direct unit tests later - thanks for calling that out :)

[axw]

jenkins run the tests please

[codecov-io]

Codecov Report

Merging #609 into master will decrease coverage by 0.06%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #609      +/-   ##
==========================================
- Coverage   87.81%   87.74%   -0.07%     
==========================================
  Files         122      122              
  Lines        7476     7476              
==========================================
- Hits         6565     6560       -5     
- Misses        810      814       +4     
- Partials      101      102       +1

Impacted Files	Coverage Δ
module/apmhttp/client.go	93.67% <66.66%> (ø)	⬆️
transport/http.go	94.27% <0%> (-1.15%)	⬇️
tracer.go	89.37% <0%> (-0.33%)	⬇️

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