sessionrecording: implement v2 recording endpoint support (#14105)

The v2 endpoint supports HTTP/2 bidirectional streaming and acks for
received bytes. This is used to detect when a recorder disappears to
more quickly terminate the session.

Updates https://github.com/tailscale/corp/issues/24023

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

k8s-operator/sessionrecording/hijacker_test.go

@@ -10,7 +10,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"net"
 	"net/http"
 	"net/netip"
 	"net/url"
@@ -20,6 +19,7 @@ import (
 	"go.uber.org/zap"
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/k8s-operator/sessionrecording/fakes"
+	"tailscale.com/sessionrecording"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tsnet"
 	"tailscale.com/tstest"
@@ -80,7 +80,7 @@ func Test_Hijacker(t *testing.T) {
 			h := &Hijacker{
 				connectToRecorder: func(context.Context,
 					[]netip.AddrPort,
-					func(context.Context, string, string) (net.Conn, error),
+					sessionrecording.DialFunc,
 				) (wc io.WriteCloser, rec []*tailcfg.SSHRecordingAttempt, _ <-chan error, err error) {
 					if tt.failRecorderConnect {
 						err = errors.New("test")