Set X-ClickHouse-Format HTTP response header to the format name

[traceon]

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Changelog category:

• Non-significant (changelog entry is not required)

Detailed description / Documentation draft:

From now on, HTTP responses will have X-ClickHouse-Format header set to the format name of the returned data.

executeQuery() callback set_content_type is renamed to set_content_type_and_format that is expected to accept 2 string arguments: content-type (as before), and format (added).

Motivation: ODBC driver can only set the default format, and has now way of reliably determining the actual format of the response (which could be modified by in-SQL FORMAT keyword), thus unable to parse, or even detect an unsupported response data format in general case.

[alexey-milovidov]

Ok.

Please mind that some formats have aliases. For example, TabSeparated = TSV.

[traceon]

Please mind that some formats have aliases. For example, TabSeparated = TSV.

@alexey-milovidov I thought it would make sense to always report the "canonical" name of the format, but it seemed to me that it would be too intrusive to expose all those getName()'s all the way to executeQuery(), so this change reports the format as it is passed in SQL or context.

[alexey-milovidov]

Ok.