Add missing sql settings

[lizsnyder]

Description of changes:

Adding missing settings per https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/user/admin/settings.rst

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[lizsnyder]

@aetter @chloe-zh for some reason it's not letting me add reviewers so tagging here for visibility

[chloe-zh]

Thanks for the changes!
I remember we have removed these settings but then added them back and deprecated them. Could you take a look to see if these settings are necessary to add to the docs accordingly? @dai-chen

[lizsnyder]

Thanks @chloe-zh. We received feedback that the “opendistro.sql.engine.new.enabled” setting must be set to true in order for the date and time SQL functions to work in Elasticsearch 7.9. Looking into that led me to realize that the setting wasn't documented in the ODFE docs. Maybe @dai-chen can shed some light on this.

[dai-chen]

These 2 settings were added later without updating the documentation. @chloe-zh I guess you said is for OpenSearch setting docs.

[chloe-zh]

LGTM, thanks!