Add avram attachment

[wout]

This is the Avram counterpart of luckyframework/lucky#2016. It adds the necessary macros and callbacks for models, save operations, and delete operations.

This PR also adds some validations for StoredFile attributes:

# MIME type
validate_file_mime_type_of avatar, in: %w[image/png image/jpeg]
validate_file_mime_type_of avatar, with: /image\/.*/

# File size
validate_file_size_of avatar, max: 5_000_000
validate_file_size_of avatar, min: 1_000, max: 5_000_000
validate_file_size_of avatar, min: 1_000

[wout]

Is the error here related to the recent work on LuckyCache?

[jwoertink]

Yeah, that's fine. Turned out that I spelled that module wrong originally 😬 So latest update fixes the typo lol. We can ignore this failure

[wout]

The latest commit here is related to the latest batch of commits on luckyframework/lucky#2016. It's a minor change.

[jwoertink]

Does this get closed now too since it's gonna move to a shard? Or do we need this?