feat: allow apps named tls

The `tls` name is no longer a reserved app name, and can be used by applications. This was previously a reserved app name due to it's use as a place for global SSL certificate files; Dokku has not supported global SSL certificates for many releases, and thus there is no need to reserve the name.

plugins/common/common.go

@@ -346,7 +346,7 @@ func DokkuApps() (apps []string, err error) {
 		if !DirectoryExists(appRoot) {
 			continue
 		}
-		if f.Name() == "tls" || strings.HasPrefix(f.Name(), ".") {
+		if strings.HasPrefix(f.Name(), ".") {
 			continue
 		}
 		apps = append(apps, f.Name())