Fetch host node assignments from the database
In preparation for variable replication factor, Praefect gained support for assigning host nodes for repositories in 243dc385.
The PerRepositoryRouter uses host assignments to determine which nodes should participate in transactions or get replicated to a given write.
This commit adds a Postgres implementation of AssignmentGetter interface. This allows the PerRepositoryRouter to get host node assignments from the database to only include assigned nodes in transactions and replications.
Related to #3154 (closed)
Edited by Sami Hiltunen