TUN-6772: Add a JWT Validator as an ingress verifier

This adds a new verifier interface that can be attached to ingress.Rule.
This would act as a middleware layer that gets executed at the start of
proxy.ProxyHTTP.

A jwt validator implementation for this verifier is also provided. The
validator downloads the public key from the access teams endpoint and
uses it to verify the JWT sent to cloudflared with the audtag (clientID)
information provided in the config.

vendor/google.golang.org/grpc/balancer/balancer.go

@@ -27,6 +27,7 @@ import (
 	"net"
 	"strings"
 
+	"google.golang.org/grpc/channelz"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/internal"
@@ -192,7 +193,7 @@ type BuildOptions struct {
 	// server can ignore this field.
 	Authority string
 	// ChannelzParentID is the parent ClientConn's channelz ID.
-	ChannelzParentID int64
+	ChannelzParentID *channelz.Identifier
 	// CustomUserAgent is the custom user agent set on the parent ClientConn.
 	// The balancer should set the same custom user agent if it creates a
 	// ClientConn.