Enable uploading of SVG images for Design Management

Problem to solve

We validate that images uploaded to design boards are in the list in Gitlab::FileTypeDetection::IMAGE_EXT.

That list excludes the svg extension as it is listed separately as a DANGEROUS_EXT.

Based on the comment above the list of DANGEROUS_EXT we would be able to enable svg, as we always supply design images with Content-Disposition: attachment.

Note that we should rename the DANGEROUS_EXT constant to IMAGE_DANGEROUS_EXT, as we want to enable just image extensions and never any non-image extensions that may be added in future.

Documentation

We should update the Design Management documentation limitations section.

Links / references