Avram::Uploadable still requires `metadata`

In https://github.com/luckyframework/lucky/pull/1513 I deprecated `metadata` because it wasn't really needed anymore. This has been deprecated for over 4 years.

But it turns out as soon as I removed that method, apps broke 😬

https://github.com/luckyframework/avram/blob/a0679823d7f6f4ae206afc83d79841f2da28adbe/src/avram/uploadable.cr#L3

This needs to be removed too, but now I'm thinking that deprecation warning was never actually showing before. I have a feeling if we remove this one, it could cause some issues ☹️

So this probably needs a deprecation warning on it now.

Start with src/avram/uploadable.cr at the referenced metadata requirement and inspect how the method is currently declared. Check the existing deprecation approach in the repository, then ensure metadata is deprecated without breaking Uploadable consumers. Done means the compatibility warning is present and the obsolete requirement can be removed safely.

Written by the indexing model from the issue text.