MINOR: stream/cli: rework "show sess" to better consider optional arguments

MINOR: stream/cli: rework "show sess" to better consider optional arguments

The "show sess" CLI command parser is getting really annoying because
several options were added in an exclusive mode as the single possible
argument. Recently some cumulable options were added ("show-uri") but
the older ones were not yet adapted. Let's just make sure that the
various filters such as "older" and "age" now belong to the options
and leave only <id>, "all", and "help" for the first ones. The doc was
updated and it's now easier to find these options.