This commit updates the KMS getting started guide
and replaces the legacy MinIO<-->Vault setup with a
MinIO<-->KES<-->Vault setup.
Therefore, add some architecture ASCII diagrams and
provide a step-by-step guide to setup Vault, KES and
MinIO such that MinIO can encrypt objects with KES +
Vault.
The legacy Vault guide has been moved to `./vault-legacy.md`.
Co-authored-by: Harshavardhana <harsha@minio.io>
