Add Support for Separate External and Internal URLs in Nextcloud

Is your feature request related to a problem? Please describe.

Currently, Nextcloud only supports a single URL field for connecting to a server. This poses a problem for users who have both external and internal access of Nextcloud, as all data traffic is routed through external servers even when the server is accessible locally. This inefficiency can be problematic, especially for users concerned about privacy and data security but even more if they have slow external connections

Describe the solution you'd like

I propose adding support for separate external and internal URLs in Nextcloud. This would allow users to specify different URLs for external access (e.g., via Cloudflare or other CDN services) and internal access (e.g., accessing the server locally). This feature would improve efficiency and privacy by enabling direct local access when possible.

Describe alternatives you've considered

One alternative is to manually switch the server URL based on the network location, but this is cumbersome and prone to errors. Another option is to use reverse proxy configurations, but this adds complexity and may not be feasible for all users, especially those with limited technical expertise or double NAT ISP.

Additional context

The Home Assistant application already implements this solution, demonstrating its feasibility and potential benefits. By adding support for separate external and internal URLs, Nextcloud can enhance user privacy, security, and efficiency, aligning with its commitment to empowering users with control over their data. Additionally, this feature would improve performance for users with low external connection speeds, as it allows them to seamlessly switch to local access when at home, mitigating the impact of slow external connections.

No files, tests, or entry points are named. First locate the existing single Nextcloud server URL setting and trace how the app chooses it for requests. Done means users can configure distinct external and internal URLs and the app can use local access when appropriate without requiring manual switching.