MINOR: sample: add missing ARGC_ entries

MINOR: sample: add missing ARGC_ entries

For a long time we couldn't have arguments in expressions used in
tcp-request, tcp-response etc rules. But now due to the variables
it's possible, and their context in case of failure to resolve an
argument (e.g. backend name not found) is not properly reported
because there is no arg context values in ARGC_* to report them.

Let's add a number of missing ones for tcp-request {connection,
session,content}, tcp-response content, tcp-check, the config
parser (for "set-var" in the global section) and the CLI parser
(for "set-var" on the CLI).