Filter on field type

[ahmednfwela]

this is a continuation on #539 and meilisearch/meilisearch#3571

I suggest adding additional filters based on field types

IS STRING, IS BOOLEAN, IS NUMBER, IS ARRAY, IS OBJECT (in addition to IS NULL and IS EMPTY)

why this is useful:

1. a common case for this is mixing arrays and non-array types, e.g.:

{"name": "book", "tags": null}
{"name": "book", "tags": "t1"}
{"name": "book", "tags": ["t1","t2"]}

a filter for tags = 't1' will return both documents, but developers might want to search for books that contain a single tag, so they can add tags = 't1' AND tags IS STRING

2. another edge case is filtering for empty strings "" only

{"name": "book", "tags": []}
{"name": "book", "tags": ""}

this query: tags IS EMPTY will match the 2 objects, but if users want to match only empty strings they can do:
tags IS STRING AND tags IS EMPTY