public QuerySettings httpHeader(String key, String value) {
        rawSettings.put(ClientConfigProperties.HTTP_HEADER_PREFIX + key, value);
        return this;
    }
Defines list of headers that should be sent with current request. The Client will use a header value
defined in {@code headers} instead of any other.

@see Client.Builder#httpHeaders(Map)
@param key - header name.
@param value - header value.
@return same instance of the builder
client-v2/src/main/java/com/clickhouse/client/api/query/QuerySettings.java