Add official support for Brave browser

### Your use case

#### What would you like to do?

Add official support for Brave browser. I suppose, latest two versions like with the other browsers.

#### Why would you like to do it?

According to one user, Brave has the best support for certain a11y tools:

> Hi,
>
> My husband has been using Element Web on Brave, but he is now getting a message that Brave is no longer supported.
>
> Can you please confirm/clarify?
>
> My husband is severely disabled and uses an eyegaze device; the Brave browser is very user-friendly for him so we would really like to continue the current arrangement if possible.
>
> Thanks.

I have let them know about the supported environments policy.

#### How would you like to achieve it?

### Have you considered any alternatives?

As Brave is Chromium based I'm guessing that it'll work just fine. But you do get the unsupported browser warning on login with eWeb Element version: 1.11.89 Crypto version: Rust SDK 0.7.2 (2f872cf), Vodozemac 0.8.1 on the latest Brave v1.73.104

### Additional context

_No response_

No source files or tests are named. Start by locating the supported-environments policy and the code that produces the unsupported-browser warning at login, then trace how browser versions are detected. Done means Brave's latest two versions are treated as supported and the warning no longer appears for them.

Written by the indexing model from the issue text.