Possibility to display the blocking page for HTTPS sites

### 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

Please add the ability to display your own page informing you that a given page has been blocked by:
- Due to detection of malware or phishing
- Due to the parental control mechanism

The browser extension already does something like this, but I would like to have this option at the DNS level - as is the case with NextDNS

This requires importing the Certificate, similarly to Next Generation Firewall solutions for SSL decryption.

### Proposed solution

Added the ability to download a certificate that will allow blockpage display on HTTPS secured websites

### Alternatives considered and additional information

_No response_