Implemented Last-Modified HTTP header metric (#407)
Implemented Last-Modified HTTP header metric (#407)

This feature returns a probe_http_last_modified metric with the content
of the Last-Modified HTTP response header, if it is set by the server.

Signed-off-by: Johannes Visintini <12066d655d4f4cec3bdedeec455995e9f58aad86@uni-heidelberg.de>
prometheus/blackbox_exporter