Str representation for integer.

[fulmicoton]

(As requested by a customer but also motivated by #3621)

Javascript (Java too?) does not play well with u64.
It would be nice to add option in the mapper to set the representation of integers as "string" for numbers.

If the option is set to false, everything happens like today. Strings as an input are rejected, and the values are encoded
as Json numbers.

If a user sets: string_in_json: true, then we would accept BOTH, strings and numbers as an input.
In addition, when we recreate JSON for documents, we would encode the values as strings.

[PSeitz]

This can be achieved with tantivy coerce option on text fields https://docs.rs/tantivy/latest/tantivy/schema/struct.TextOptions.html#method.set_coerce
It would store the numbers as string internally though, not sure if that is desired.

[guilload]

Can we decouple ingestion and search and go with the parameters that we already use for other fields: input_formats and output_format?

[fulmicoton]

That makes sense, although in this very case, there is very little upside to not allowing both string and number.
input_formats is not as important.

[guilload]

Closed via #3704.