Add file downloading

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Checklist

• [X] There are no similar issues or pull requests for this yet.

Is your feature related to a problem? Please describe.

I want to have the possibility to download files from the admin panel

Describe the solution you would like.

If string is filepath than you can download it

Additional context

I already have solutions to resolve my problem. And I made a pull request for it. Please check and give me feedback. https://github.com/aminalaee/sqladmin/pull/702