Use ubus for authentication for better integration with OpenWRT luci

### Prerequisites

- [X] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [X] I have searched other issues and found no duplicates

- [X] I want to request a feature or enhancement and not ask a question

### The problem

With AdGuardHome running on an openwrt router, I need to separately log into openwrt and adguardhome's web interfaces, which is inconvenient.

### Proposed solution

I search the codebase and noticed there is a special "GLMode" authentication, which reads a token file from `/tmp`:

https://github.com/AdguardTeam/AdGuardHome/blob/1d6d85cff4bf5915156f28d07582b4f0bb359d04/internal/home/authglinet.go#L17

GL-Inet turns out to be a [router manufacturer](https://www.gl-inet.com/), so I assume this mode is so that users that have logged into the router's interface don't have to log into AGH again.

I think OpenWRT can get similar treatment. OpenWRT's web interface uses ubus for authentication, and all current sessions can be listed by running `ubus call session list` on the router. So in theory AGH can use ubus to check if a session token is valid or not.

### Alternatives considered and additional information

_No response_