Add 'Strict Sequence' order to upstream DNS servers

### 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 Upstream DNS servers support 3 different types of behaviour `Load Balancing, Parallel, Fastest IP`.

Could support for `strict sequential order` also be added to the same?

The next upstream DNS server would only be used if the first one has failed to respond.
This would make it inline with **dnsmasq** configuration option of `strict-order`; thereby **the DNS upstreams are used in the order listed**.

This allows upstream DNS servers redundancy to be deployed more effectively.

### Proposed solution

Add a 4th option to Upstream DNS servers. Maybe call it `Strict Sequence`.

### Alternatives considered and additional information

_No response_