rclone config redacted: implement support mechanism for showing redacted config

This introduces a new fs.Option flag, Sensitive and uses this along
with IsPassword to redact the info in the config file for support
purposes.

It adds this flag into backends where appropriate. It was necessary to
add oauthutil.SharedOptions to some backends as they were missing
them.

Fixes #5209

backend/smb/smb.go

@@ -41,13 +41,15 @@ func init() {
 		NewFs:       NewFs,
 
 		Options: []fs.Option{{
-			Name:     "host",
-			Help:     "SMB server hostname to connect to.\n\nE.g. \"example.com\".",
-			Required: true,
+			Name:      "host",
+			Help:      "SMB server hostname to connect to.\n\nE.g. \"example.com\".",
+			Required:  true,
+			Sensitive: true,
 		}, {
-			Name:    "user",
-			Help:    "SMB username.",
-			Default: currentUser,
+			Name:      "user",
+			Help:      "SMB username.",
+			Default:   currentUser,
+			Sensitive: true,
 		}, {
 			Name:    "port",
 			Help:    "SMB port number.",
@@ -57,9 +59,10 @@ func init() {
 			Help:       "SMB password.",
 			IsPassword: true,
 		}, {
-			Name:    "domain",
-			Help:    "Domain name for NTLM authentication.",
-			Default: "WORKGROUP",
+			Name:      "domain",
+			Help:      "Domain name for NTLM authentication.",
+			Default:   "WORKGROUP",
+			Sensitive: true,
 		}, {
 			Name: "spn",
 			Help: `Service principal name.
@@ -71,6 +74,7 @@ authentication, and it often needs to be set for clusters. For example:
 
 Leave blank if not sure.
 `,
+			Sensitive: true,
 		}, {
 			Name:    "idle_timeout",
 			Default: fs.Duration(60 * time.Second),