feat: add support for script and upsert on ES output

[gfyrag]

Add some capabilities to elasticsearch output :

• Support for scripted update
• Support for "upsert" in updates

The new behavior is enabled setting the property 'multipart' to true on the output. Once the 'multipart' defined, 3 new fields are evaluated :

• doc: replace the root
• script: add the "script" field
• upsert: add "upsert" field

See the documentation : https://www.elastic.co/guide/en/elasticsearch/reference/7.0/docs-update.html#_literal_doc_as_upsert_literal

[flemzord]

Any news @Jeffail ?