chore: Rework resolver flow for modules

[valentindeaconu]

This PR reworks the resolver flow for modules.

Tasks:

• Extract URL downloading from resolvers (their job is to manage the storage, not to download files);
• Rework the file package to work with files in memory (since their content is required to be uploaded to the remote storage);

The go-getter implementation was also reworked since the old implementation was not suitable for providers (checksum mismatch, the reason for #14)

• Move resolver logic from the repository to service for modules;
• Update ModuleService.Upload signature to take the URL as argument, preparing it to also accept InMemoryFiles (file uploading - subject of a future PR);