Allow sentry user to control resolution of captured Flutter screenshots

[cstavitsky]

Feature request: Allow Sentry users to control the resolution at which Flutter screenshots are captured by Sentry, allow the Sentry user to control the resolution at which screenshots are captured.

For example, Sentry's Unity SDK currently allows users to select among:

• as is
• high - 1920p
• medium - 720p
• low - 420p

The request is to allow similar choice in resolution for Flutter screenshots.

• There is concern that larger-resolution screenshots may cause bandwidth problems for events captured on low-end mobile devices and regions with poor cellular connectivity. The thought is that being able to adjust resolution would help with this.

┆Issue is synchronized with this Jira Improvement by Unito

[marandaneto]

We can add the max resolution to SentryFlutterOptions and allow users to change it during SDK init.
https://api.flutter.dev/flutter/rendering/RenderRepaintBoundary/toImage.html
Maybe the pixelRatio is enough, if not, we can likely manipulate the returned Image.
IIRC Unity has this already, so let's align on the naming and format @bitsandfoxes if possible.

[bitsandfoxes]

IIRC Unity has this already, so let's align on the naming and format @bitsandfoxes if possible.

The Unity SDK went with ScreenshotQuality

public enum ScreenshotQuality
{
    Full,
    High,
    Medium,
    Low
}

Which translates into max dimension while keeping the aspect ratio

return quality switch
{
    ScreenshotQuality.High => 1920,     // 1080p
    ScreenshotQuality.Medium => 1280,   // 720p
    ScreenshotQuality.Low => 854,       // 480p
    _ => 854                            // Fallback
};