Reduce JWT overhead for internode tokens (#13738)

Since JWT tokens remain valid for up to 15 minutes, we 
don't have to regenerate tokens for every call.

Cache tokens for matching access+secret+audience 
for up to 15 seconds.

```
BenchmarkAuthenticateNode/uncached-32         	  270567	      4179 ns/op	    2961 B/op	      33 allocs/op
BenchmarkAuthenticateNode/cached-32           	 7684824	       157.5 ns/op	      48 B/op	       1 allocs/op
```

Reduces internode call allocations a great deal.

cmd/jwt_test.go

@@ -21,6 +21,7 @@ import (
 	"net/http"
 	"os"
 	"testing"
+	"time"
 
 	jwtgo "github.com/golang-jwt/jwt/v4"
 	"github.com/minio/minio/internal/auth"
@@ -224,11 +225,22 @@ func BenchmarkAuthenticateNode(b *testing.B) {
 	}
 
 	creds := globalActiveCred
-	b.ResetTimer()
-	b.ReportAllocs()
-	for i := 0; i < b.N; i++ {
-		authenticateNode(creds.AccessKey, creds.SecretKey, "")
-	}
+	b.Run("uncached", func(b *testing.B) {
+		fn := authenticateNode
+		b.ResetTimer()
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			fn(creds.AccessKey, creds.SecretKey, "aud")
+		}
+	})
+	b.Run("cached", func(b *testing.B) {
+		fn := cachedAuthenticateNode(time.Second)
+		b.ResetTimer()
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			fn(creds.AccessKey, creds.SecretKey, "aud")
+		}
+	})
 }
 
 func BenchmarkAuthenticateWeb(b *testing.B) {