Improve error logging of JSON insert api failure - "unsupported value type"

[bZichett]

Is your feature request related to a problem? Please describe.
Moreso a very easy improvement to aid in awareness of what the particular violation is

Describe the solution you'd like
Include the field name that failed validation and the value that caused the failure. For bulk json updates, it'd be great to include at the ID of the document that caused failure. These three additions would be completely sufficient.

manticoresearch/src/sphinxjsonquery.cpp

Line 1049 in b78ca03

sError = "unsupported value type";

Above is where the following error message is produced.

HTTP response headers: HTTPHeaderDict({'Server': '6.0.2 [...])', 'Content-Type': 'application/json; charset=UTF-8', 'Content-Length': '34'})  
HTTP response body: {"error":"unsupported value type"}  

The aspecificity is pretty unhelpful since I am using the bulk update to API to index thousands of documents at once (nearly positive the issue I am having is with an unexpected nulll field.) And there is a bit of friction for me to narrow down the problem here.

[sanikolaev]

Thanks. We'll think what we can do with it.

[sanikolaev]

It's unlikely we'll be able to refer to the document ID, but what we can improve is to at least point to a specific line in the bulk input.

[klirichek]

Fixed in 87a0f3b
See commit message for details