User Cache Invalidation becomes a little trickier to reason about in invisible sharding, since we have colocated routers and shards. We should write tests to ensure that user cache invalidation works on the following topologies:

1/ Single Shard Cluster with colocated router and config
2/ Two Shard Cluster with shard A having colocated router and config and shard B having colocated router.

We should specifically test the following invalidation scenarios:

1/ Invalidation through the LDAPUserCachePoller
2/ Invalidation through updating configurations of the IDPManager
3/ Invalidation through the UserCacheInvalidator job on the router