[apmhttp] WithClientSpanType ClientOption

[Jasonfran]

Hi,

This is a pull request to add a WithClientSpanType option when wrapping an http.Client

I've come across a few instances in the past where I want to better differentiate my HTTP requests. For example when calling into a Varnish cache over HTTP, I'd rather it have the "cache" span type. There are some cases where I have HTTP requests that are better classified as database requests, so I'd like the "db" span type.

Currently the workaround is to grab the span off the context and set the span type before closing the response body. It works, but it's not particularly elegant. That's why I think this new ClientOption would be useful.

I did the change before making an issue asking about it since it's a tiny change

Let me know 😄

---

By the way, TestFilesystemContextSetter and TestFilesystemContextSetterFileNotFound don't seem to work on my machine. It's a Windows machine. They result in these test failures:

=== RUN   TestFilesystemContextSetter
    context_test.go:91: ContextLine differs:   string(
        - 	`	panic("context!")`,
        + 	"\tpanic(\"context!\")\r",
          )
--- FAIL: TestFilesystemContextSetter (0.00s)

=== RUN   TestFilesystemContextSetterFileNotFound
    context_test.go:91: ContextLine differs:   string(
        - 	`	panic("context!")`,
        + 	"\tpanic(\"context!\")\r",
          )
--- FAIL: TestFilesystemContextSetterFileNotFound (0.00s)

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• Start Time: 2021-08-26T00:43:01.527+0000

• Duration: 32 min 21 sec

• Commit: 4545713

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Failed	0
Passed	11023
Skipped	268
Total	11291

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[axw]

Looks good, thanks @Jasonfran! Would you please add a short entry in CHANGELOG.asciidoc?

Not sure what's up with the tests on Windows, but that's essentially defunct code that we're keeping around to avoid breaking the API. I wouldn't worry about it.

[Jasonfran]

Thanks @axw I've updated the CHANGELOG.asciidoc, I think I've done it correctly. Does the docs/upgrading.asciidoc file need updating too?

[axw]

Just a minor issue with the changelog update. Thanks and sorry, I should have given some guidance on how to update it! We will move things from "unreleased" to a new version when a new version is released.

[Jasonfran]

Hi, I think that's done now?

[axw]

LGTM, thanks for the PR :)