Add back rr.ImageEncoded for backwards compatibility

[emilk]

What

• Closes Add back old rr.ImageEncoded helper to guide users #7086
• Should maybe wait for Introduce new ImageFormat component #7083

I need someone with Python skills to finish this.

Note that these are revived things:

• https://ref.rerun.io/docs/python/0.17.0/common/enums/#rerun.ImageFormat
• https://ref.rerun.io/docs/python/0.17.0/common/image_helpers/

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
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[github-actions]

Deployed docs

Commit	Link
35375ed	https://landing-8sneny5ja-rerun.vercel.app/docs

[emilk]

ImageEncoded used to be a class, but is now a function so that it can return either an Image or an EncodedImage. Maybe a Python guru has a better idea?

[emilk]

This warning makes the unit tests fail. I have no idea how to fix that.