[Doc][Meta] Improvements to output-elasticsearch docs

[karenzone]

Improvements to documentation

• Add note about _type change from doc to _doc [Doc]Add note about _type setting change from doc to _doc #884
• Request for "more explicit documentation for both upsert and doc_as_upsert" in [Doc]Add more explicit documentation for upsert and doc_as_upsert #928
• Fix index default value [Doc]Fix default value for index and bump to v.10.4.0 #927

[karenzone]

Continued in #978