Adapt replication plugin dependencies to its new api package

The ReplicationConfig and other related classes are now part of the
replication-api plugin and need to be accessed on its own package.

Also adapt to the recent changes in Gerrit and replication plugin
on the master branch.

Depends-On: https://gerrit-review.googlesource.com/c/plugins/replication/+/407431
Change-Id: I5cce6943b424bfc89ab3b690e305ebc34f452d5d