fix(config): default.user not set in cofnig.toml, add --assume-yes to dnf mod list

[shigechika]

What did you implement:

• Bypass with -assumeyes when dnf module list stoped at GPG key import prompt appeared.

• Fix to use ssh default user when server.user is empty.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist:

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• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
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• Update the messages below

Is this ready for review?: YES

[kotakanbe]

LGTM

[kotakanbe]

It works correctly with the below config.

[default]
    port = "22"
    scanMode = ["fast"]
    user = "ec2-user"

[servers]
[servers.rhel8]
host = "3.112.204.xxx"
keyPath = "/home/ubuntu/.ssh/stg.pem"
scanMode = ["fast"]

[servers.localhost]
host = "localhost"
port = "local"
scanMode = ["fast"]