fix: add image processor disabled flag with alternate processor

[Aerilym]

SESSION_DISABLE_IMAGE_PROCESSOR=1 environment variable to disable the use of the image processor. Generated link preview images will no longer work and display pictures are limited to non-animated images.

[Copilot]

Pull request overview

This PR adds a feature flag disableImageProcessor to disable the main image processor and provide a fallback implementation using the Canvas API. This allows the application to continue processing avatar images even when the main image processor is disabled or unavailable.

• Added disableImageProcessor feature flag with environment variable support
• Implemented Canvas-based fallback image processor for avatar processing
• Added error handling to catch image processor failures and use the fallback

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
ts/state/ducks/types/releasedFeaturesReduxTypes.ts	Added disableImageProcessor boolean feature flag to the type definition
ts/state/ducks/types/defaultFeatureFlags.ts	Configured default value for disableImageProcessor based on environment variable SESSION_DISABLE_IMAGE_PROCESSOR
ts/webworker/workers/browser/image_processor_interface.ts	Added feature flag check to throw error when image processor is disabled
ts/util/avatar/processAvatarData.ts	Implemented processImageFallback using Canvas API and added try-catch to fall back when main processor fails

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