AQL: add dbal sql processor

[alekitto]

Add "raw" SQL processor based on doctrine DBAL query builder.
It is meant to be used if low-level data retrieval is needed (query a view, use of a custom db extension) or where an ORM should/could not be used.

Comparing to ORM and ODM ones, it has some few limitations:

• There is no auto-mapping of fields, all the selected fields need to be selected with select method on query builder prior to the initialization of the Processor
• $entry support is limited. Due to the lack of a schema, there's no support to an automatic join mechanism
• To fully support pagination (with continuation token), the SQL built via query builder will be wrapped as a subquery in the FROM clause
• Result iterator emits associative arrays instead of objects
• Results are emitted as emitted from PDO. No conversion will be made on the returned result.

[massimilianobraglia]

Hey there @alekitto! Thanks for this great feature!
Just left some comments on it!

Sorry about the late reply 😓

[alekitto]

I've converted the Dbal namespaces to uppercase and left replies to the other comments.

[alekitto]

👍 All done

[massimilianobraglia]

Thank you, @alekitto!