re-write the KMS get started guide (#8936)

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>

docs/kms/vault-config.json

@@ -1,5 +1,5 @@
 {
-  "api_addr": "http://127.0.0.1:8200",
+  "api_addr": "https://127.0.0.1:8200",
   "backend": {
     "file": {
       "path": "vault/file"
@@ -10,8 +10,9 @@
   "listener": {
     "tcp": {
       "address": "0.0.0.0:8200",
-      "tls_disable": true
+      "tls_cert_file": "vault-tls.crt",
+      "tls_key_file": "vault-tls.key",
+      "tls_min_version": "tls12"
     }
-  },
-  "ui": true
+  }
 }