Load ProjectLevelConfig directly

Cache introduced in [1] (in 3.3.1) prevents using getAllProjects().getConfig(...)
from Gerrit Core to read serviceuser db file.

To overcome this, we need to read config directly, bypassing the cache.

[1] https://gerrit-review.googlesource.com/c/gerrit/+/275992

Change-Id: I9b4b1e66cf8e2b41059997bb53ebeeaba7ee3ea3