Renameable binaries / path

ko defaults to placing binaries into the path /ko-app/<app-name>. As for now it seems as if there is no way to set this name during the build process.

This is especially important if the containers are used in a Kubernetes environment where the entrypoint is overwritten and the absolute path of the binary is important, which is a common practice.

Although this path might be known it complicates the drop-in integration of ko containers in a production environment, since the deployments have to be adjusted to use the ko specific path.

The lines responsible for the naming seem to be these.

It would be great if a new flag such as -o / --out-path or something similar could be introduced that let the user set the output path to their needs.