Allow users to upload key file in the setup

[le-git-imate]

Description of issue or feature request
le-git-imate allows users to import keys as text. It can add an option to upload the key file.

Current behavior

• le-git-imate does not allow to add an existing key file into the keyring by uploading the key file.

Expected behavior

• Allow to import existing keys either as file or as text.
• Allow the user to upload multiple key files