net/http/pprof: update the /debug/pprof endpoint

- Documented the duration parameter in Profile() to match with Trace().

- Properly handling the error from strconv.ParseInt to match with Trace().

- Updated the profiles tables to include additional handlers exposed from
net/http/pprof. Added a separate section at the bottom to explain what
the profiles are and how to use them.

Fixes #24380

Change-Id: I8b7e100d6826a4feec81f29f918e7a7f7ccc71a0
Reviewed-on: https://go-review.googlesource.com/112495


Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>