Capture mime-types and supported extensions as part of the storage configuration

[dcousens]

As discussed in #6715

In @keystone-6/core <= 5.7.0, unfortunately we are quite opinionated about what mime-types we support as part of the file and image fields.

We should update the configuration to support a user-prescribed list of mime types, in a way that the users can apply their project's security considerations and restrictions.
We should have some warnings around any common pitfalls, but that should be documentation.

Existing Signal 📶

• Adding SVG in image types available for upload #6715
• File Preview not possible #8538
• Image type extension not supporting svg #8203

[erreib]

Was curious if there had been any changes or movement on this? Or alternatively if anyone had implemented a custom field that allowed for svg uploads?