no "CLIENT-SUBNET" in "OPT pseudosection", result in broken ECS support when using AGH as upstream

### 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

query from AGH with custom subnet:
`dig IN A @dns.mydns.com www.google.com +subnet=3.80.0.0/24 -p5353`

```
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;www.google.com. IN A

;; ANSWER SECTION:
```

while query from unbound with the same subnet info (unbound is on the same machine with different port):
`dig IN A @dns.mydns.com www.google.com +subnet=3.80.0.0/24 -p53`

```
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; CLIENT-SUBNET: 3.80.0.0/24/12
;; QUESTION SECTION:
;www.google.com. IN A

;; ANSWER SECTION:
```
without the "CLIENT-SUBNET" part, AGH can't handle ECS cache correctly just as described here
[https://github.com/AdguardTeam/AdGuardHome/issues/5757#issuecomment-1525560081](url)
that is said, i can't use another AGH as my AGH's upstream, which will result in broken ECS function

### Proposed solution

there is "CLIENT-SUBNET" part in "OPT pseudosection", which will be telling the downstream AGH to cache ECS correctly

### Alternatives considered and additional information

_No response_