SQL: rename DataType.DATE to something else

[costin]

While respecting the Elasticsearch type naming, Es-SQL has a DATE type which in practice is a DateTime.
However this clashes with the SQL type DATE causing a lot of confusion especially when migrating.

Several options were discussed going forward:

1. rename date

Rename date to datetime. This adds more meaning to the content however breaks the convention that it maps the elasticsearch date type.
On the upside there's no collision with the SQL types and allows the SQL date type if needed.

2. rename date to timestamp

This is a variant of 1 however it follows the SQL terminology which might be both confusing and clear.

3. don't expose ES types in the queries

Prevent the problem from exposing by not allowing the user to create the ES data types (typically through CAST - CAST ('1' AS KEYWORD). This will impact testing and be asymmetric since such types are returned as results. Further more, the confusion around date remains since it shows up in the table description.

[elasticmachine]

Pinging @elastic/es-search

[costin]

/cc @eskibars

[costin]

FTR, the plan is to rename DATE to DATETIME to better indicate its structure while keeping it short. This also doesn't clash with any other data type and while it won't match the naming in Elasticsearch, it won't clash with SQL DATE either.