[Headless CMS] Wrong label on file field input

[Pavel910]

What steps will reproduce the bug?

Create a new content model, and add a File field. Switch to the Preview tab, and you'll see Select an image label. This is wrong, because it assumes that only an image can be selected, but in fact, it can be any asset.

What is the expected behavior?

I guess a better label would be Select a file or Select an asset. If the File field is configured to only allow images, then we can use the Select an image label.