Report slowest frames of renderMedia() #1344

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There is already a function for finding the slowest chunks inside renderMediaOnLambda(), but it would be useful to measure each single frame in renderMedia() and return the slowest frames so one can optimize the render times of it.

Acceptance criteria:

• Measure the time for each frame and store it in-memory, e.g. in a JavaScript object
• Make sure to free up the memory afterwards to not create a memory leak
• Make renderMedia() return an object of which one of the properties is slowestFrames, which returns the 10 slowest frames (if there are any)
• In the cli package, grab that information, and print the slowest frames using Log.verbose
• In the lambda package, in renderer.ts, log the slowest frames as well.
• Add documentation to render-media.md describing the feature and mention the version it's going to be available in (current version + 0.0.1)