Alow `remotePollInterval` option to be set server side

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### Feature description

https://docs.nextcloud.com/desktop/latest/advancedusage.html#configuration-file

`remotePollInterval` is a very important setting when dealing with high server density (many users and many files/folders).
Being able to set it in the server `config.php` file (like `remote_poll_interval = > 1632477`) would be a very good adition for server admins to spread that value to **all** clients.

Logic:

1. Try the remote server value `remote_poll_interval`,
2. If unset or null, fallback to any locally configured (or default) value.