doc: zbus: adjust documentation to comply with iterable section observers

Add details of the new VDED sequence;
Change the function iterators documentation considering `user_data`;
Adjust the runtime observers' allocation information. Now it uses heap
instead of memory slabs;
Adjust the configuration list and details of it.

Signed-off-by: Rodrigo Peixoto <rodrigopex@gmail.com>
1 file changed