fix: correctly validate root credentials from secret

[twelho]

When using the MinIO operator to deploy a tenant, the operator-deployed sidecar container keeps crashing on startup:

2024/03/31 22:02:42 sidecar.go:48: Starting Sidecar
2024/03/31 22:03:28 sidecar.go:171: Missing root credentials in the configuration.
2024/03/31 22:03:28 sidecar.go:172: MinIO won't start

This occurs when deploying https://github.com/minio/operator/tree/master/helm/tenant, even with default values, with a configuration secret in the same form as the automatically generated one:

apiVersion: v1
kind: Secret
metadata:
  name: myminio-env-configuration
stringData:
  config.env: |-
    export MINIO_ROOT_USER="minio"
    export MINIO_ROOT_PASSWORD="minio123"
type: Opaque

After a bunch of messing around with the configuration I figured out that this is a bug introduced in https://github.com/minio/operator/pull/1437. Regardless of the configuration provided in the secret, the following check will always fail due to rootUserMissing := true, and even if that is fixed, it will still fail unless all four of the supported environment variables are defined, even though AFAICT they are supposed to be either-or (user/pass or access/secret):

https://github.com/minio/operator/blob/a6a3e21dc7c0e9cac88b12a6fed63e8cce8308d1/pkg/sidecar/sidecar.go#L153-L174

This PR fixes the issue by copying the intended logic from validator.go:

https://github.com/minio/operator/blob/a6a3e21dc7c0e9cac88b12a6fed63e8cce8308d1/pkg/validator/validator.go#L110-L128

Tested working in a bare-metal deployment.

Two questions remain:

• How has this not been caught for over a year at this point? I'm beginning to doubt whether the operator is production-ready. Am I doing something incorrectly?
• There are three identical instances of the Missing root credentials in the configuration. termination in the code without a way to easily distinguish between them from stdout. Maybe a proper logging framework could be of use here?