Add user-agent header to ocsp stapling request

[mlibbey]

Currently the ocsp stapling requests do not have a User-Agent header assigned. It would be nice to add one that contains something about ATS ... proxy.config.http.response_via_str; proxy.config.product_name; just hardcode ATS ... something :). Presumably it would be another add1_header near

trafficserver/iocore/net/OCSPStapling.cc

Line 382 in 40c3d57

OCSP_REQ_CTX_add1_header(ctx, "Host", host);