skaffold init should not fail on existing skaffold.yaml if it's pointing to another skaffold.yaml

[balopat]

When an existing skaffold.yaml might be overriden by the skaffold init execution we should warn the user. This is why we throw an error: pre-existing skaffold.yaml found (you may continue with --force)

This should be avoided when the target configuration is a different file from the existing skaffold.yaml file, e.g.:

• the file is in a different directory
• -f different_skaffold.yaml is passed in

Also, if --analyze passed in, we can ignore this error, as skaffold is not writing a skaffold.yaml file.