SQL: Consider adding the columnar option for the returned results

[astefan]

At the moment ES-SQL adopts a row based approach for returning the results, meaning a list of lists where each sub-list contains one value for each column/field.

The columnar approach, on the other hand, returns all values of a certain column in a single list. Still to be decided if all the variants of clients (ODBC, JDBC, REST etc) and formats (json, yaml, txt, csv etc) make sense for this feature.

[elasticmachine]

Pinging @elastic/es-search

[monfera]

Kibana Canvas functions involving common renderers that use column JSONs themselves would benefit, as there'd be no need to expensively transpose big arrays in the browser, besides the all-around gain of better compressibility (due to negligible [ ] and lower , noise; serially adjacent data likely having the same format; common parts or, in the case of ordered output, identical values)

[astefan]

master (8.0.0): 5b7e0de
7.x (7.1.0): 4deb69e

@monfera this is merged with the soonest available version - 7.1.0.