[DOCS] Fixed typos in aggregations.asciidoc

Fix plural/singular forms.
[DOCS] fixed typo in date-format.asciidoc
[DOCS] Fixed the fuzzy query docs with correct default value max_expansion option
[DOCS] Fixed typo in put-mapping docs

split backwardscompatibility to backwards compatibility
make this new test a bit less stressful for nightly; catch FlushNotAllowedEngineException