…tic#89074)

* Add search source to example plugin.

* Add uiSetting for fields API.

* Update SearchSource to support fields API.

* [PoC] reading from the fields API in Discover

* Add N fields as a default column

* Make fields column non-removeable

* Do not add 'fields' to state

* Remove fields from app state and read from source when needed

* Remove fields column if a new column is added

* Add search source to example plugin.

* Add uiSetting for fields API.

* Update SearchSource to support fields API.

* Improve error handling in search examples plugin.

* Add unit tests for legacy behavior.

* Remove uiSettings feature flag; add fieldsFromSource config.

* Rewrite flatten() based on final API design.

* Update example app based on final API design.

* Update maps app to use legacy fieldsFromSource.

* Update Discover to use legacy fieldsFromSource.

* Rename source filters to field filters.

* Address feedback.

* Update generated docs.

* Update maps functional test.

* Formatting fields column similar to _source

* Moving logic for using search API to updating search source

* Fix small merge error

* Move useSource switch to Discover section of advanced settings

* Do not use fields and source at the same time

* Remove unmapped fields switch

* Add basic support for grouping multifields

* Remove output.txt

* Fix some merge leftovers

* Fix some merge leftovers

* Fix merge errors

* Fix typescript errors and update nested fields logic

* Add a unit test

* Fixing field formats

* Fix multifield selection logic

* Request all fields from source

* Fix eslint

* Fix default columns when switching between _source and fields

* More unit tests

* Update API changes

* Add unit test for discover field details footer

* Remove unused file

* Remove fields formatting from index pattern

* Remove unnecessary check

* Addressing design comments

* Fixing fields column display and renaming it to Document

* Adding more unit tests

* Adding a missing check for useNewFieldsAPI; minor fixes

* Fixing typescript error

* Remove unnecessary console statement

* Add missing prop

* Fixing import order

* Adding functional test to test fields API

* [Functional test] Clean up in after

* Fixing context app

* Addressing PR comments

* Add support for unmapped fields

* Add data migration

* Add toggle unmapped fields logic

* Adding more unit tests

* Some cleanup

* More unit tests

* Fixing failing snapshot

* Add tooltip next to unmapped switch

* Add functional test for the feature

* Fixing a typo in a functional test

* Refetch data when unmapped fields value changes

* Updating mapping

* Support for fields API in search embeddable

* Addressing PR comments

* Fix failing unit test

* Updating the text

Co-authored-by: Luke Elmers <luke.elmers@elastic.co>
Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>