Changes:
* Condenses and relocates the `docvalue_fields` example to the 'Run a search'
page.
* Adds docs for the `docvalue_fields` request body parameter.
* Updates several related xrefs.
Co-authored-by: debadair <debadair@elastic.co>
Several APIs support options that can be specified as a query parameter or a
request body parameter.
Currently, this is documented using notes, which can get rather lengthy. This
replaces those multiple notes with a single note and a footnote.
James Rodewig