incidentd: creating PolicyProto for NotificationManager

The previous code saved a String in the proto like
"NotificationManager.Policy[priorityCategories=PRIORITY_CATEGORY_REMINDERS,PRIORITY_CATEGORY_EVENTS,PRIORITY_CATEGORY_MESSAGES,PRIORITY_CATEGORY_CALLS,PRIORITY_CATEGORY_REPEAT_CALLERS,priorityCallSenders=PRIORITY_SENDERS_STARRED,priorityMessageSenders=PRIORITY_SENDERS_STARRED,suppressedVisualEffects=SUPPRESSED_EFFECT_SCREEN_OFF]".
This unfortunately would mean that the String would have to be parsed on
the server-side, which kinda defeats the purpose of migrating to protos,
so I made a proto for this :)

BUG: 65750824
Test: flash device and check incident.proto output, comparing it to the previous output
Change-Id: I87607dc7b72ce3519132da23167b4bdce3b7ef4c