policy: log selected actions

Rebased on top of !1234 (merged) (but planned to merge to master after EDE gets there)

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The following actions will now be logged in debug level (or request tracing): ANSWER, DENY, DENY_MSG, DROP, REFUSE, TC

This can be useful for RPZ and other policy debugging.

Purposefully ommitted actions:

• PASS - since it's the same as normal processing
• REROUTE - the action itself comes from renumber module
• STUB,FORWARD,TLS_FORWARD - this could be more confusing than useful (e.g. when response comes from cache)

Fixes #689 (closed)