Remove auto_create_index / SavedObjectsClient/autoCreateIndex error and error view

[rudolf]

In #14271 Kibana started using an index template and auto-creating the index when the first saved object is created. After the saved object migrations system was introduced, Kibana started explicitly creating a saved object when the process is started, so we can remove this functionality from server & public.

kibana/src/core/server/saved_objects/types.ts

Lines 159 to 166 in 97d1685

	* ### 503s from missing index
	*
	* Unlike all other methods, create requests are supposed to succeed even when
	* the Kibana index does not exist because it will be automatically created by
	* elasticsearch. When that is not the case it is because Elasticsearch's
	* `action.auto_create_index` setting prevents it from being created automatically
	* so we throw a special 503 with the intention of informing the user that their
	* Elasticsearch settings need to be updated.

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)