Prometheus metrics missing

The sealed secrets controller does not expose all the metrics in the metrics namespace "sealed_secrets_controller_" it should according to the ode in https://github.com/bitnami-labs/sealed-secrets/blob/v0.15.0/cmd/controller/metrics.go.
```
$ curl -s 127.0.0.1:8080/metrics | egrep 'sealed_secrets_controller_'
# HELP sealed_secrets_controller_build_info Build information.
# TYPE sealed_secrets_controller_build_info gauge
sealed_secrets_controller_build_info{revision="v0.15.0"} 0
# HELP sealed_secrets_controller_unseal_requests_total Total number of sealed secret unseal requests
# TYPE sealed_secrets_controller_unseal_requests_total counter
sealed_secrets_controller_unseal_requests_total 2
```
Especiall missing the "unseal_errors_total" metric.