Is your feature request related to a problem? Please describe.
It'd be useful to set a custom UA for identifying desktop apps. Additionally, some sites require UA spoofing to work.

Describe the solution you'd like
Add a way to allow setting a custom UA for a webview.

Describe alternatives you've considered
N/A

Would you assign yourself to implement this feature?

• Yes
• No

Additional context
N/A

I'd like to make an attempt at adding this feature, the main question I have is whether it's reasonable to implement it as a property on WebViewBuilder and InnerWebView::new, or if there is a better place.