MAINTAINERS: add tracepoint core-api doc files to TRACING

The files in Documentation/core-api/ are by virtue of their top-level
directory part of the Documentation section in MAINTAINERS. Each file in
Documentation/core-api/ should however also have a further section in
MAINTAINERS it belongs to, which fits to the technical area of the
documented API in that file.

The tracepoint.rst provides some explanation to tracepoints defined in
selected files under include/trace/events/, which itself is part of the
TRACING section.

So, add this core-api document to TRACING.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251105092428.153378-1-lukas.bulwahn@redhat.com
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: bulwahn

MAINTAINERS

@@ -26464,6 +26464,7 @@ L:	linux-trace-kernel@vger.kernel.org
 S:	Maintained
 Q:	https://patchwork.kernel.org/project/linux-trace-kernel/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
+F:	Documentation/core-api/tracepoint.rst
 F:	Documentation/trace/*
 F:	fs/tracefs/
 F:	include/linux/trace*.h