This commit changes the config/IAM encryption
process. Instead of encrypting config data
(users, policies etc.) with the root credentials
MinIO now encrypts this data with a KMS - if configured.
Therefore, this PR moves the MinIO-KMS configuration (via
env. variables) to a "top-level" configuration.
The KMS configuration cannot be stored in the config file
since it is used to decrypt the config file in the first
place.
As a consequence, this commit also removes support for
Hashicorp Vault - which has been deprecated anyway.
Signed-off-by: Andreas Auernhammer <aead@mail.de>