MINOR: sample: Add fetcher for getting all cookie names

MINOR: sample: Add fetcher for getting all cookie names

This new fetcher can be used to extract the list of cookie names from
Cookie request header or from Set-Cookie response header depending on
the stream direction. There is an optional argument that can be used
as the delimiter (which is assumed to be the first character of the
argument) between cookie names. The default delimiter is comma (,).

Note that we will treat the Cookie request header as a semi-colon
separated list of cookies and each Set-Cookie response header as
a single cookie and extract the cookie names accordingly.