[IMPROVED] Add legacy api warnings on old JetStream API (#1553)

Signed-off-by: Piotr Piotrowski <piotr@synadia.com>

js.go

@@ -32,6 +32,11 @@ import (
 )
 
 // JetStream allows persistent messaging through JetStream.
+//
+// NOTE: JetStream is part of legacy API.
+// Users are encouraged to switch to the new JetStream API for enhanced capabilities and
+// simplified API. Please refer to the `jetstream` package.
+// See: https://github.com/nats-io/nats.go/blob/main/jetstream/README.md
 type JetStream interface {
 	// Publish publishes a message to JetStream.
 	Publish(subj string, data []byte, opts ...PubOpt) (*PubAck, error)
@@ -106,6 +111,11 @@ type JetStream interface {
 }
 
 // JetStreamContext allows JetStream messaging and stream management.
+//
+// NOTE: JetStreamContext is part of legacy API.
+// Users are encouraged to switch to the new JetStream API for enhanced capabilities and
+// simplified API. Please refer to the `jetstream` package.
+// See: https://github.com/nats-io/nats.go/blob/main/jetstream/README.md
 type JetStreamContext interface {
 	JetStream
 	JetStreamManager
@@ -276,6 +286,11 @@ const (
 
 // JetStream returns a JetStreamContext for messaging and stream management.
 // Errors are only returned if inconsistent options are provided.
+//
+// NOTE: JetStreamContext is part of legacy API.
+// Users are encouraged to switch to the new JetStream API for enhanced capabilities and
+// simplified API. Please refer to the `jetstream` package.
+// See: https://github.com/nats-io/nats.go/blob/main/jetstream/README.md
 func (nc *Conn) JetStream(opts ...JSOpt) (JetStreamContext, error) {
 	js := &js{
 		nc: nc,