docs: pm: Update runtime PM documentation and release notes

Add new configuration options for runtime PM to the release notes,
including stack size, priority, and system work queue usage. Update
the runtime PM documentation to explain the implications of using the
system work queue and disabling asynchronous operations. Include a new
version of the sequence diagram for asynchronous operations.

Signed-off-by: Flavio Ceolin <flavio@hubblenetwork.com>