docs: admin-guide: clarify perf bench all behavior

docs: admin-guide: clarify perf bench all behavior

The workload tracing guide lists a fixed set of benchmarks for
"perf bench all". This list is stale and can become outdated when
perf adds, removes, or renames benchmark collections or individual
benchmarks.

Describe "perf bench all" as running all available benchmarks in the perf
bench framework instead. Also document how to list the collections and
benchmarks available on a given system.

Signed-off-by: Cheng-Han Wu <hank20010209@gmail.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260503101429.254394-4-hank20010209@gmail.com>