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/rand/rand.go

@@ -0,0 +1,31 @@
+package rand
+
+import (
+	"crypto/rand"
+	"fmt"
+	"io"
+	"math/big"
+)
+
+func init() {
+	Reader = rand.Reader
+}
+
+// Reader provides a random reader that can reset during testing.
+var Reader io.Reader
+
+// Int63n returns a int64 between zero and value of max, read from an io.Reader source.
+func Int63n(reader io.Reader, max int64) (int64, error) {
+	bi, err := rand.Int(reader, big.NewInt(max))
+	if err != nil {
+		return 0, fmt.Errorf("failed to read random value, %w", err)
+	}
+
+	return bi.Int64(), nil
+}
+
+// CryptoRandInt63n returns a random int64 between zero and value of max
+// obtained from the crypto rand source.
+func CryptoRandInt63n(max int64) (int64, error) {
+	return Int63n(Reader, max)
+}