OSF: Used model.NewPointer everywhere (#27838)

```release-note
NONE
```

server/channels/api4/system_test.go

@@ -137,27 +137,27 @@ func TestEmailTest(t *testing.T) {
 	es := model.EmailSettings{}
 	es.SetDefaults(false)
 
-	es.SMTPServer = model.NewString("")
-	es.SMTPPort = model.NewString("")
-	es.SMTPPassword = model.NewString("")
-	es.FeedbackName = model.NewString("")
-	es.FeedbackEmail = model.NewString("some-addr@test.com")
-	es.ReplyToAddress = model.NewString("some-addr@test.com")
-	es.ConnectionSecurity = model.NewString("")
-	es.SMTPUsername = model.NewString("")
-	es.EnableSMTPAuth = model.NewBool(false)
-	es.SkipServerCertificateVerification = model.NewBool(true)
-	es.SendEmailNotifications = model.NewBool(false)
-	es.SMTPServerTimeout = model.NewInt(15)
+	es.SMTPServer = model.NewPointer("")
+	es.SMTPPort = model.NewPointer("")
+	es.SMTPPassword = model.NewPointer("")
+	es.FeedbackName = model.NewPointer("")
+	es.FeedbackEmail = model.NewPointer("some-addr@test.com")
+	es.ReplyToAddress = model.NewPointer("some-addr@test.com")
+	es.ConnectionSecurity = model.NewPointer("")
+	es.SMTPUsername = model.NewPointer("")
+	es.EnableSMTPAuth = model.NewPointer(false)
+	es.SkipServerCertificateVerification = model.NewPointer(true)
+	es.SendEmailNotifications = model.NewPointer(false)
+	es.SMTPServerTimeout = model.NewPointer(15)
 
 	config := model.Config{
 		ServiceSettings: model.ServiceSettings{
-			SiteURL: model.NewString(""),
+			SiteURL: model.NewPointer(""),
 		},
 		EmailSettings: es,
 		FileSettings: model.FileSettings{
-			DriverName: model.NewString(model.ImageDriverLocal),
-			Directory:  model.NewString(dir),
+			DriverName: model.NewPointer(model.ImageDriverLocal),
+			Directory:  model.NewPointer(dir),
 		},
 	}
 
@@ -573,14 +573,14 @@ func TestS3TestConnection(t *testing.T) {
 	fs := model.FileSettings{}
 	fs.SetDefaults(false)
 
-	fs.DriverName = model.NewString(model.ImageDriverS3)
-	fs.AmazonS3AccessKeyId = model.NewString(model.MinioAccessKey)
-	fs.AmazonS3SecretAccessKey = model.NewString(model.MinioSecretKey)
-	fs.AmazonS3Bucket = model.NewString("")
-	fs.AmazonS3Endpoint = model.NewString(s3Endpoint)
-	fs.AmazonS3Region = model.NewString("")
-	fs.AmazonS3PathPrefix = model.NewString("")
-	fs.AmazonS3SSL = model.NewBool(false)
+	fs.DriverName = model.NewPointer(model.ImageDriverS3)
+	fs.AmazonS3AccessKeyId = model.NewPointer(model.MinioAccessKey)
+	fs.AmazonS3SecretAccessKey = model.NewPointer(model.MinioSecretKey)
+	fs.AmazonS3Bucket = model.NewPointer("")
+	fs.AmazonS3Endpoint = model.NewPointer(s3Endpoint)
+	fs.AmazonS3Region = model.NewPointer("")
+	fs.AmazonS3PathPrefix = model.NewPointer("")
+	fs.AmazonS3SSL = model.NewPointer(false)
 
 	config := model.Config{
 		FileSettings: fs,
@@ -599,18 +599,18 @@ func TestS3TestConnection(t *testing.T) {
 		// If this fails, check the test configuration to ensure minio is setup with the
 		// `mattermost-test` bucket defined by model.MINIO_BUCKET.
 		*config.FileSettings.AmazonS3Bucket = model.MinioBucket
-		config.FileSettings.AmazonS3PathPrefix = model.NewString("")
+		config.FileSettings.AmazonS3PathPrefix = model.NewPointer("")
 		*config.FileSettings.AmazonS3Region = "us-east-1"
 		resp, err = th.SystemAdminClient.TestS3Connection(context.Background(), &config)
 		require.NoError(t, err)
 		CheckOKStatus(t, resp)
 
-		config.FileSettings.AmazonS3Region = model.NewString("")
+		config.FileSettings.AmazonS3Region = model.NewPointer("")
 		resp, err = th.SystemAdminClient.TestS3Connection(context.Background(), &config)
 		require.NoError(t, err)
 		CheckOKStatus(t, resp)
 
-		config.FileSettings.AmazonS3Bucket = model.NewString("Wrong_bucket")
+		config.FileSettings.AmazonS3Bucket = model.NewPointer("Wrong_bucket")
 		resp, err = th.SystemAdminClient.TestS3Connection(context.Background(), &config)
 		CheckInternalErrorStatus(t, resp)
 		CheckErrorID(t, err, "api.file.test_connection_s3_bucket_does_not_exist.app_error")
@@ -1054,7 +1054,7 @@ func TestCheckHasNilFields(t *testing.T) {
 
 	t.Run("check if the struct has any nil fields", func(t *testing.T) {
 		s := model.FileSettings{
-			DriverName: model.NewString(model.ImageDriverLocal),
+			DriverName: model.NewPointer(model.ImageDriverLocal),
 		}
 		res := checkHasNilFields(&s)
 		require.True(t, res)