REGTESTS: sample_fetches: add a test for the HTTP response fetches

REGTESTS: sample_fetches: add a test for the HTTP response fetches

Almost none of the res.* sample fetches was covered. This test checks
status, txn.status, res.ver, res.hdr, res.hdr_val, res.hdr_ip,
res.hdr_cnt with an occurrence index, res.hdr_names with and without a
custom delimiter, res.fhdr and res.fhdr_cnt against res.hdr on a
comma-delimited list, res.cook, res.cook_cnt, res.cook_val,
res.cook_names, res.body_size, res.hdrs, res.hdrs_bin, res.comp,
res.comp_algo and res.timer.hdr, as well as the deprecated shdr, shdr_val,
shdr_ip, shdr_cnt, scook, scook_cnt, scook_val and resp_ver aliases, and
the capture.res.hdr and capture.res.ver fetches fed by a response header
capture.