Custom TTL for Domain Resolution in AdGuard Home

### 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

Many users, including myself, experience unnecessary DNS resolutions for domains that have infrequent IP changes. In my case, I manage a domain whose IP address rarely changes, yet the current TTL forces repeated DNS lookups. This results in extra processing overhead and network traffic that could otherwise be minimized.

### Proposed solution

I propose adding an option within AdGuard that allows users to set a custom TTL (Time-To-Live) for specific domains. By enabling a higher TTL for domains with stable IP addresses, AdGuard could reduce the frequency of DNS lookups, thereby lowering processing loads and minimizing network traffic. This feature would provide enhanced flexibility and allow users to optimize their configurations based on their individual network environments.

### Alternatives considered and additional information

While caching mechanisms and DNS prefetching exist as general solutions, they do not offer granular control over TTL values on a per-domain basis. A custom TTL setting would empower users to tailor the DNS resolution behavior specifically for each domain, ensuring optimal performance and efficiency in various scenarios. Contributions should adhere to the repository's contributing guidelines and security policy.