Single Binary without metrics generator logs "value is nil" repeatedly

[joe-elliott]

When running the single binary the following is logged repeatedly if the metrics generator is not configured:

level=info ts=2023-02-01T14:18:57.573201626Z caller=client.go:255 msg="value is nil" key=collectors/metrics-generator index=81

This is an innocuous but annoying error message. The root cause is our change to drop the metrics_generator_enabled setting. In the single binary deployment an in memory kv store is used for ring propagation. The metrics generator module is never created and therefore never creates the key that the client expects.