[Docs] Reformat exported fields documentation (elastic#12242)

* [Docs] Remove extraneous section levels from field docs

* Clean up headings to make content easier to scan

* Move description and run make update

* Rebase and run make update

* Removed old commented out section from script

* Rebase and run make update

* Rebase and run make update

* Fix code formatting and run make update

* Fixing python script formatting to make pep8 linter happy