Add ImageExport renderer for playwright-dotnet

Description

As plotly.js, the underlying library that Plotly.NET is using needs an environment that can execute javascript to render images programmatically.

https://github.com/microsoft/playwright-dotnet seems to be another stable, mature option for automating tasks on a headless browser.

Pointers

• A reference implementation for this using PuppeteerSharp can be seen here

首先阅读 src/Plotly.NET.ImageExport/PuppeteerSharpRenderer.fs，这是图像导出的参考实现。在研究 playwright-dotnet API 之前，使用它来了解预期的渲染器结构。完成的标准是：playwright-dotnet 有可用的同等 ImageExport 渲染器，并且现有的图像导出行为仍受支持。