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/middleware.go

@@ -0,0 +1,71 @@
+package middleware
+
+import (
+	"context"
+)
+
+// Handler provides the interface for performing the logic to obtain an output,
+// or error for the given input.
+type Handler interface {
+	// Handle performs logic to obtain an output for the given input. Handler
+	// should be decorated with middleware to perform input specific behavior.
+	Handle(ctx context.Context, input interface{}) (
+		output interface{}, metadata Metadata, err error,
+	)
+}
+
+// HandlerFunc provides a wrapper around a function pointer to be used as a
+// middleware handler.
+type HandlerFunc func(ctx context.Context, input interface{}) (
+	output interface{}, metadata Metadata, err error,
+)
+
+// Handle invokes the underlying function, returning the result.
+func (fn HandlerFunc) Handle(ctx context.Context, input interface{}) (
+	output interface{}, metadata Metadata, err error,
+) {
+	return fn(ctx, input)
+}
+
+// Middleware provides the interface to call handlers in a chain.
+type Middleware interface {
+	// ID provides a unique identifier for the middleware.
+	ID() string
+
+	// Performs the middleware's handling of the input, returning the output,
+	// or error. The middleware can invoke the next Handler if handling should
+	// continue.
+	HandleMiddleware(ctx context.Context, input interface{}, next Handler) (
+		output interface{}, metadata Metadata, err error,
+	)
+}
+
+// decoratedHandler wraps a middleware in order to to call the next handler in
+// the chain.
+type decoratedHandler struct {
+	// The next handler to be called.
+	Next Handler
+
+	// The current middleware decorating the handler.
+	With Middleware
+}
+
+// Handle implements the Handler interface to handle a operation invocation.
+func (m decoratedHandler) Handle(ctx context.Context, input interface{}) (
+	output interface{}, metadata Metadata, err error,
+) {
+	return m.With.HandleMiddleware(ctx, input, m.Next)
+}
+
+// DecorateHandler decorates a handler with a middleware. Wrapping the handler
+// with the middleware.
+func DecorateHandler(h Handler, with ...Middleware) Handler {
+	for i := len(with) - 1; i >= 0; i-- {
+		h = decoratedHandler{
+			Next: h,
+			With: with[i],
+		}
+	}
+
+	return h
+}