rbd: add aws-sts-metdata encryption type

With Amazon STS and kubernetes cluster is configured with
OIDC identity provider, credentials to access Amazon KMS
can be fetched using oidc-token(serviceaccount token).
Each tenant/namespace needs to create a secret with aws region,
role and CMK ARN.
Ceph-CSI will assume the given role with oidc token and access
aws KMS, with given CMK to encrypt/decrypt DEK which will stored
in the image metdata.

Refer: https://docs.aws.amazon.com/STS/latest/APIReference/welcome.html
Resolves: #2879

Signed-off-by: Rakshith R <rar@redhat.com>

vendor/github.com/aws/smithy-go/document.go

@@ -0,0 +1,10 @@
+package smithy
+
+// Document provides access to loosely structured data in a document-like
+// format.
+//
+// Deprecated: See the github.com/aws/smithy-go/document package.
+type Document interface {
+	UnmarshalDocument(interface{}) error
+	GetValue() (interface{}, error)
+}