Extract routing logic in to a separate component

Routing logic is currently not pluggable as it is part of the coordinator and depends on the NodeManager. In preparation for variable replication factor and per repository primary, this commit extracts the routing logic in to a separate component which allows for plugging in alternative implementation. There should be no behavior difference, except for eagerly loading consistent secondaries on repository scoped mutators regardless of whether transactions are enabled or not. This should be fine though as transactions are enabled by default.

Refactoring related to #2971 (closed)