sched_deadline, docs: replace rt-app examples with chrt or use config.json

sched_deadline, docs: replace rt-app examples with chrt or use config.json

rt-app no longer accepts command-line arguments. So, replace rt-app example
with chrt and use the JSON format in the other example instead of command-
line arguments.

Signed-off-by: Shashank Balaji <shashank.mahadasyam@sony.com>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250527-sched-deadline-cpu-affinity-v2-1-b8b40a4feefa@sony.com