feat(installer)!: remove the --update-nginx flag (#2851)

### Description

Related to #2543

BREAKING CHANGE: The `--update-nginx` flag was removed from the
installer. The nginx configuration deployed by the installer will now
always be overwritten. Make sure to move your customizations to a
reverse proxy configuration.
libretime/libretime@35d7eac

docs/admin-manual/install/install-using-the-installer.md

@@ -131,12 +131,6 @@ When upgrading be sure to run the installer using the same arguments you used du
 
 :::
 
-:::warning
-
-To update the LibreTime nginx configuration file, for example to change the `--listen-port`, make sure to add the `--update-nginx` flag to allow overwriting the existing configuration file.
-
-:::
-
 If you need to change some configuration, the install script can be configured using flags or environment variables. Changing the listening port of LibreTime or whether you want to install some dependency by yourself, you could run the following:
 
 ```bash