Fixed #9757 - Added model uploads

[snipe]

This adds a file upload option to asset models.

Next Steps:

• Rename the AssetFileRequest to be more generic
• Possibly Traitify files so that there's less repetition
• Add files endpoint to API so we can BS tables those mofos

Fixes #9757 and FD-28554

[uberbrady]

This looks SUPER clean, very nice. Should be a great feature. I had a couple of comments about the use of file_get_contents() - I think the Storage facade gives us some more 'fluent' ways of approaching those files. But that's not enough of a big deal to stop the PR. I'm super-excited about all these great new features we're adding, all throughout!