* Add a REST integration test that documents date_range support
Add a test case that exercises date_range aggregations using the missing
option.
Addresses #17597
* Test cleanup and correction
Adding a document with a null date to exercise `missing` option, update
test name to something reasonable.
* Update documentation to explain how the "missing" parameter works for
date_range aggregations.
* Wrap lines at 80 chars in docs.
* Change format of test to YAML for readability.
This adds the `VIEW IN CONSOLE` and `COPY AS CURL` links to the
snippets in the docs for the `date_range` aggregation and tests
those snippets as part of the build.
Relates to #18160
