DOC: design: add notes about more detailed error reporting for logs

DOC: design: add notes about more detailed error reporting for logs

These are the notes of a day long code analysis session (CFA+WTA)
aimed at figuring what's missing during most code troubleshooting
sessions.  The goal is to provide good indications about what rules/
filters were still active when the processing ended (timeout, error
etc), what subscribers are still active (indicating waiting for an
event), and what shut/abort events were met at the various levels
of each side's stack, in each direction.