Migrate AdGuard Home wiki to this Knowledge Base

AdGuard Home Wiki markdown files available by cloning the repo: `https://github.com/AdguardTeam/AdGuardHome.wiki.git`

The problem with the Github Wiki is that it does not support localization unlike the DNS knowledge base.

As for why keeping AG DNS and AdGuard Home together, I suppose there are many common topics and thus it makes sense to keep them together.

The task itself should be done in several smaller pull requests.

Please structure the process the following way:
1. Create a branch named `adguardhome`.
2. Create new branches from that branch.
3. Create pull requests **to that branch**.
4. Once we have all content finalized in that branch, we'll create a new pull request to the master branch.

Please ask @ainar-g help and add them to every pull request.

A few notes about the work itself:

1. Add a new section to the knowledge base and call it "AdGuard Home".
2. AdGuard Home wiki often has "internal" manually written tables of contents. We don't need them as Docusaurus builds them automatically.
3. Do not follow the same markdown style when migrating the content, rely on auto-beautify by VS code. Sorry @ainar-g, the reason for that is that I am almost sure that Crowdin won't play well with the guidelines you're using now as Crowdin will ruin it completely when re-importing the content.

Once this work is finished and the KB is live, we'll start changing the existing AdGuard Home wiki and funnel people to the new location.