rename vault namespace env variable to be more idiomatic (#6905)

This commit renames the env variable for vault namespaces
such that it begins with `MINIO_SSE_`. This is the prefix
for all Minio SSE related env. variables (like KMS).

cmd/crypto/vault.go

@@ -193,7 +193,7 @@ func NewVault(kmsConf KMSConfig) (KMS, error) {
 		return nil, err
 	}
 
-	if ns, ok := os.LookupEnv("VAULT_NAMESPACE"); ok {
+	if ns, ok := os.LookupEnv("MINIO_SSE_VAULT_NAMESPACE"); ok {
 		c.SetNamespace(ns)
 	}
 

docs/kms/README.md

@@ -69,9 +69,9 @@ Optionally set `MINIO_SSE_VAULT_CAPATH` as the path to a directory of PEM-encode
 export MINIO_SSE_VAULT_CAPATH=/home/user/custom-pems
 ```
 
-Optionally set `VAULT_NAMESPACE` if AppRole and Transit Secrets engine have been scoped to Vault Namespace
+Optionally set `MINIO_SSE_VAULT_NAMESPACE` if AppRole and Transit Secrets engine have been scoped to Vault Namespace
 ```
-export VAULT_NAMESPACE=ns1
+export MINIO_SSE_VAULT_NAMESPACE=ns1
 ```
 ### 4. Test your setup