docs: relocate Resque config option comments to render in Yard docs

[robbkidd]

As formatted markdown comments on the class, the information is made visible in the Yard-generated docs without making the options appear to be class or instance variables. Possibly instrumentation READMEs could link in the Usage section to the instrumentation's latest version at rubydoc.info (for example, this here resque) to avoid repeating the details of config options in the README but still making the options discoverable from there.

Placing all this on the Instrumentation class is in contrast to the approach used in #824 where each option has a distinct comment.

Advantages to class-level doc comment:

1. The option names do not appear to be class or instance methods on Instrumentation within the documentation.
2. The documentation can be included and rendered higher up the module namespace (on OTel::Inst::Resque) with a single line while the doc content still lives close(ish) to the option declarations.
3. Simpler than holding Yard macros the right way.

Disadvantages to class-level doc comment:

1. The documentation is a little removed from the option declarations.

Screenshots!

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[arielvalentin]

Since this is going to help your customers I think that getting this merged will be ok with me, however per our slack conversations I think longer term what we want is a way to document individual options and then somehow render them in the README.