Remove `protection_disabled_until` from configuration

### 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

The config file (/etc/adguardhome.yaml in OpenWRT), contains two keys:

```
filtering:
protection_disabled_until:
protection_enabled:
```

which save the "disabled" state of AGH and (if necessary) the expiry of the disabled state of AGH.

I consider this to be "dynamic runtime data" that shouldn't live in a config file. There are two (imo negative) implications at the moment:

1. This transient data causes false "backups" and config versions.
2. In embedded systems that use flash, it causes a working write (which OpenWRT at least tries to minimise).

I think it can be removed without breaking functionality (or perhaps changing the behaviour in a positive way).

### Proposed solution

For `protection_disabled_until`: Remove the key, and keep the value in memory. This means a reboot during the window will likely cause AGH to be enabled again. I think this lies within expectations. However if we really want to keep that expiry across restarts then the value can be kept in a file in the temp filesystem (as applicable).

For `protection_enabled`: only set this if AGH is disabled without a timer. My expectation is that this isn't often and not transient, so writing this case to config would be reasonable.

### Alternatives considered and additional information

_No response_