Added HeadlessPluginContext, Canvas3DRenderer, image-renderer example (#700)

* Added HeadlessPluginContext, Canvas3DRenderer, image-renderer example

* Fixed dependencies in package.json

* Removed gl from deps

* Removed gl, pngjs, jpeg-js from dependencies, importing via LazyImports

* Updated docs in src/examples/image-renderer/index.ts

* Added gl, pngjs, jpeg-js to optionalDependencies

* Canvas3DRenderer: default cameraResetDurationMs: 0 (necessary when changing camera between renderings)

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Co-authored-by: David Sehnal <dsehnal@users.noreply.github.com>