Fix animation not preserved to GIFs in case of AUTO_WEBP

[vaniyokk]

Issue #456

Description of changes: Add WEBP ContentTypes.WEBP to list of formats that supports animation (and should preserve animation on compressed image)

Checklist

• [ ] :wave: I have added unit tests for all code changes.
• [x] :wave: I have run the unit tests, and all unit tests have passed.
• [x] :warning: This pull request might incur a breaking change.

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[dougtoppin]

@vaniyokk Thank you for your submission. We will evaluate the change and get back to you.

[simonkrol]

Hi @vaniyokk

We've finished evaluating this change and have decided to include it in the next minor/major release. To avoid affecting existing deployments, the current plan is that overriding whether an image should be animated will be done with /filters:animated(true/false) or edits: { animated: true }, which will override the existing GIF type check (maintaining the existing behaviour if the animated filter is not provided). While our internal processes have us merge the code manually, once the release with this change is out, you'll see yourself included in the external contributors section towards the bottom of the readme and this PR will be closed.

Thanks for your contributions, Simon

[simonkrol]

Change has been included in v6.2.6, thanks for your contributions :)