net/http: add request file upload benchmarks
net/http: add request file upload benchmarks

This adds benchmarks to test file uploads using PUT requests.

It's designed to complement changes https://golang.org/cl/163599 and
https://golang.org/cl/163737, allowing an easy comparison of
performance before and after these changes are applied.

Updates #30377.

Co-authored-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

Change-Id: Ib8e692c61e1f7957d88c7101669d4f7fb8110c65
GitHub-Last-Rev: 242622b4fca9f289defa2f268efc31208743e5dd
GitHub-Pull-Request: golang/go#30424
Reviewed-on: https://go-review.googlesource.com/c/go/+/163862
Run-TryBot: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,akutz/go,akutz/go,CAFxX/go,akutz/go,golang/go,cloudflare/go,josharian/go,josharian/go,akutz/go,cloudflare/go,CAFxX/go,golang/go,cloudflare/go,cloudflare/go,golang/go,josharian/go,akutz/go,CAFxX/go,golang/go,akutz/go,nawawi/go,nawawi/go,cloudflare/go,josharian/go,akutz/go,CAFxX/go,CAFxX/go,nawawi/go,CAFxX/go,josharian/go,golang/go,josharian/go,nawawi/go,CAFxX/go,golang/go,akutz/go,nawawi/go,josharian/go,golang/go,golang/go,nawawi/go,josharian/go,CAFxX/go,cloudflare/go