Add information about beta in settings

[rakleed]

Issue Details

Now, in order to try new features and check out fixes in the beta version, the user needs to find information on where and how to install it.

Proposed solution

Add information about the beta to the settings and a link to how you can install it: https://adguard-vpn.com/en/beta.html?platform=browser_extension

Alternative solution

No response

[alexx7311]

Thanks! We'll think about it.