This commit adds a serializer for the NotifyConfig entitiy.
The eventual goal is that we serialize CachedProjectConfig. The
entity is too large to be serialized directly, though, so we
divide and conquer.
This commit moves the AutoValue representation to the entities
package to allow the serializer packages to keep its dependencies
minimal.
Change-Id: I6876624bbe5d99c3ca187984f1214bf2066850fa
9b15b9ce00