Opentracing Documentation (#5703)

* Opentracing survival guide

* Update decorator names in doc

* Doc cleanup

These are all alterations as a result of comments in #5703, it
includes mostly typos and clarifications. The most interesting
changes are:

- Split developer and user docs into two sections
- Add a high level description of OpenTracing

* newsfile

* Move contributer specific info to docstring.

* Sample config.

* Trailing whitespace.

* Update 5703.misc

* Apply suggestions from code review

Mostly just rewording parts of the docs for clarity.

Co-Authored-By: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>