DoH/3 DNS upstream can be added in the native implementation mode

### Version
AdGuard for iOS 4.5 (1002)

### Environment
iPhone XS, 16.5.1

### Steps to reproduce
1. Launch AdGuard
2. Open the Protection tab -> DNS protection screen -> DNS implementation
3. Switch the implementation from AdGuard to `Native`
4. Go to DNS server screen
5. Scroll down and click the `Add a custom DNS server`
6. Enter any server name
7. Enter `h3://dns.adguard-dns.com/dns-query` in the DNS server address field
8. Tap the `Save` button

### Expected behaviour
The error message "DNS-over-HTTPS/3 is not supported by the system" is displayed.
Similar to when trying to add DoQ upstreams.

Error message for DoQ upstreams


### Actual behaviour

DNS server has been added and selected successfully