## What changed?
- Set default priority on all internalTasks after creation.
- Combine effective priority and poll forwarder flag into one value.
- For simplicity, default priority and level count are set at partition
load time.
## Why?
Tasks with unset priority key were not actually getting the default
value when read from backlog. This sets the default priority on all
sync, backlog, query, and nexus tasks. (Priority is not meaningful for
sync match tasks, and nexus has no priority yet, but they're set anyway
for consistency.) This will also make it easier to adjust the priority
for other purposes, e.g. prioritizing the old backlog for migrating
persistence.
## How did you test it?
- [x] built
- [x] run locally and tested manually
- [x] covered by existing tests
- [ ] added new unit test(s)
- [x] modified functional test
