upgrade: Split in two steps to ensure a stable retry (#15396)

Currently, if one server in a distributed setup fails to upgrade 
due to any reasons, it is not possible to upgrade again unless 
nodes are restarted.

To fix this, split the upgrade process into two steps :

- download the new binary on all servers
- If successful, overwrite the old binary with the new one

go.mod

@@ -51,7 +51,7 @@ require (
 	github.com/minio/madmin-go v1.4.3
 	github.com/minio/minio-go/v7 v7.0.32
 	github.com/minio/pkg v1.1.26
-	github.com/minio/selfupdate v0.4.0
+	github.com/minio/selfupdate v0.5.0
 	github.com/minio/sha256-simd v1.0.0
 	github.com/minio/simdjson-go v0.4.2
 	github.com/minio/sio v0.3.0