Add body_size_limit option to http module (#836)

Add body_size_limit option to http module (#836)

This option limits the maximum body length that will be read from the
HTTP server. It's meant to prevent misconfigured servers from causing
the probe to use too many resources, even if temporarily. It's not an
additional check on the response, for that, use the resulting metrics
(probe_http_content_length, probe_http_uncompressed_body_length, etc).

Co-authored-by: Julien Pivotto <roidelapluie@inuits.eu>