fix: recommended setting for redis when using 1 replica

[nleconte-csgroup]

Hello,

To use only 1 replicas, we need to update the redis configuration min-replicas-to-write to 0 otherwise we have the error message "NOREPLICAS Not enough good replicas to write".

Ref: https://stackoverflow.com/a/59737862

Note: It's well configured in the CI : https://github.com/oauth2-proxy/manifests/blob/3832a76bd98c42d787da8e2069ecdbdda45c4b5f/helm/oauth2-proxy/ci/redis-standalone-values.yaml#L29 It's just missing in the doc