Breaking API change: applications can set a User-Agent prefix

[jayohms]

This resolves issues like these:

• Empty bridge-components in default userAgent #64
• Hotwire.registerBridgeComponents() doesn't set user agent #68

Applications can now set a custom applicationUserAgentPrefix for their application via:

Hotwire.config.applicationUserAgentPrefix = "My Application Prefix"

Whenever a WebView instance is created, the library will now automatically include:

• Your (optional) custom applicationUserAgentPrefix
• "Hotwire Native Android; Turbo Native Android;"
• "bridge-components: [your bridge components];"
• The WebView's default Chromium user agent string

Since this a breaking API change, we'll include this is in an upcoming v1.1 release.