Shorten the way to the system DNS settings for Native DNS implementation

### Problem Description

Currently, once we turn on/off the AdGuard DNS, there is a pop-up with the path of DNS setting.

### Proposed Solution

For iOS 15, the url scheme is:
- Launch from Widget: prefs:root=General&path=ManagedConfigurationList/DNS
- Launch from App: App-prefs:root=General&path=ManagedConfigurationList/DNS
(please let me know if there is a deeper url for DNS page)

For iOS 10(?) ~ iOS 14:
- Prefs:root=VPN/DNS
- App-prefs:root=VPN/DNS

For iOS 10 (?) and earlier:
- Prefs:root=General&path=Network/VPN

Reference:
- https://www.macstories.net/ios/a-comprehensive-guide-to-all-120-settings-urls-supported-by-ios-and-ipados-13-1/
- https://github.com/phynet/iOS-URL-Schemes