Add ButterCMS image provider support #46

Feature Title

Add ButterCMS image provider support

Description

Add a documented ButterCMS image integration by reusing the Filestack transformation implementation proposed in “Add Filestack image provider support” #12

Use Case

A ButterCMS-backed application needs responsive image URLs for media delivered through its documented Filestack pipeline.

Proposed Solution

• If a named buttercms integration is added, export and register it in core for shared Angular, React, and Svelte configuration. Keep the implementation in its base provider.
• Complete the Filestack provider first, then verify it against ButterCMS’s published media URL and transformation examples.
• Provide a buttercms wrapper or alias only where configuration or source normalization differs. Otherwise, publish a ButterCMS-specific Filestack configuration recipe.
• Keep task serialization in the Filestack implementation, preserve source identifiers and existing transformations, and document any relevant source or signing restrictions.
• Add setup documentation and focused fixtures covering ButterCMS media URLs, source normalization, shared task serialization, and documented modifier examples. Validate advertised dimensions and content types against an enabled service or controlled server where applicable.

Alternatives Considered

Use the proposed Filestack provider directly or construct ButterCMS transformation URLs manually. A separate transformation engine would duplicate the documented Filestack contract.

Examples from Other Libraries

• Not found
• Image editing and transformations
• Image transformation API