This substantially reduces the number of API calls made by the endpoint
controller. Currently the controller makes an API call per endpoint for
each service that is synced. When the 30s resync is triggered, this
results in an API call for every single endpoint in the cluster. This
quickly exceeds the default qps/burst limit of 20/30 even in small
clusters, leading to delays in endpoint updates.

This change modifies the controller to use the endpoint informer cache
for all endpoint GETs. This means we only make API calls for changes in
endpoints. As a result, qps only depends on the pod activity in the
cluster, rather than the number of services.