Documentation: tracing: Add documentation about eprobes

Eprobes was added back in 5.15, but was never documented. It became a
"secret" interface even though it has been a topic of several
presentations. For some reason, when eprobes was added, documenting it
never became a priority, until now.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/20250730140945.528135548@kernel.org


Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>