Ease use of Chromium-based browsers

[aryzing]

Is your feature request related to a problem? Please describe.
On systems that use Chromium-based browsers other than Chrome, WXT fails to start with the error

The CHROME_PATH environment variable must be set to a Chrome/Chromium executable no older than Chrome stable.

Describe the solution you'd like

Provide

• an option to configure the browser's path
• an enhanced error message

For the browser path,

• consider a WXT-specific env variable such as WXT_BROWSER_PATH
• consider an option to set the path in wxt.config.ts

For the enhanced error message,

• reference to the docs on how to set up a custom browser path (assuming the above suggestion is implemented)
• add a short snippet example on how to run with alternative browsers, such as: CHROME_PATH=$(which brave-browser) npm run dev