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/encoding/xml/map.go

@@ -0,0 +1,53 @@
+package xml
+
+// mapEntryWrapper is the default member wrapper start element for XML Map entry
+var mapEntryWrapper = StartElement{
+	Name: Name{Local: "entry"},
+}
+
+// Map represents the encoding of a XML map type
+type Map struct {
+	w       writer
+	scratch *[]byte
+
+	// member start element is the map entry wrapper start element
+	memberStartElement StartElement
+
+	// isFlattened returns true if the map is a flattened map
+	isFlattened bool
+}
+
+// newMap returns a map encoder which sets the default map
+// entry wrapper to `entry`.
+//
+// A map `someMap : {{key:"abc", value:"123"}}` is represented as
+// `<someMap><entry><key>abc<key><value>123</value></entry></someMap>`.
+func newMap(w writer, scratch *[]byte) *Map {
+	return &Map{
+		w:                  w,
+		scratch:            scratch,
+		memberStartElement: mapEntryWrapper,
+	}
+}
+
+// newFlattenedMap returns a map encoder which sets the map
+// entry wrapper to the passed in memberWrapper`.
+//
+// A flattened map `someMap : {{key:"abc", value:"123"}}` is represented as
+// `<someMap><key>abc<key><value>123</value></someMap>`.
+func newFlattenedMap(w writer, scratch *[]byte, memberWrapper StartElement) *Map {
+	return &Map{
+		w:                  w,
+		scratch:            scratch,
+		memberStartElement: memberWrapper,
+		isFlattened:        true,
+	}
+}
+
+// Entry returns a Value encoder with map's element.
+// It writes the member wrapper start tag for each entry.
+func (m *Map) Entry() Value {
+	v := newValue(m.w, m.scratch, m.memberStartElement)
+	v.isFlattened = m.isFlattened
+	return v
+}