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/middleware/metadata.go

@@ -0,0 +1,65 @@
+package middleware
+
+// MetadataReader provides an interface for reading metadata from the
+// underlying metadata container.
+type MetadataReader interface {
+	Get(key interface{}) interface{}
+}
+
+// Metadata provides storing and reading metadata values. Keys may be any
+// comparable value type. Get and set will panic if key is not a comparable
+// value type.
+//
+// Metadata uses lazy initialization, and Set method must be called as an
+// addressable value, or pointer. Not doing so may cause key/value pair to not
+// be set.
+type Metadata struct {
+	values map[interface{}]interface{}
+}
+
+// Get attempts to retrieve the value the key points to. Returns nil if the
+// key was not found.
+//
+// Panics if key type is not comparable.
+func (m Metadata) Get(key interface{}) interface{} {
+	return m.values[key]
+}
+
+// Clone creates a shallow copy of Metadata entries, returning a new Metadata
+// value with the original entries copied into it.
+func (m Metadata) Clone() Metadata {
+	vs := make(map[interface{}]interface{}, len(m.values))
+	for k, v := range m.values {
+		vs[k] = v
+	}
+
+	return Metadata{
+		values: vs,
+	}
+}
+
+// Set stores the value pointed to by the key. If a value already exists at
+// that key it will be replaced with the new value.
+//
+// Set method must be called as an addressable value, or pointer. If Set is not
+// called as an addressable value or pointer, the key value pair being set may
+// be lost.
+//
+// Panics if the key type is not comparable.
+func (m *Metadata) Set(key, value interface{}) {
+	if m.values == nil {
+		m.values = map[interface{}]interface{}{}
+	}
+	m.values[key] = value
+}
+
+// Has returns whether the key exists in the metadata.
+//
+// Panics if the key type is not comparable.
+func (m Metadata) Has(key interface{}) bool {
+	if m.values == nil {
+		return false
+	}
+	_, ok := m.values[key]
+	return ok
+}