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/io/reader.go

@@ -0,0 +1,16 @@
+package io
+
+import (
+	"io"
+)
+
+// ReadSeekNopCloser wraps an io.ReadSeeker with an additional Close method
+// that does nothing.
+type ReadSeekNopCloser struct {
+	io.ReadSeeker
+}
+
+// Close does nothing.
+func (ReadSeekNopCloser) Close() error {
+	return nil
+}