Allow specifying multiple builds that reference the same dir/main, then specify which build ID when running ko build

[ari-becker]

Feature request: allow specifying multiple builds that reference the same dir/main, then specify which build ID when running ko build, e.g. ko build --build-id=foo.

Why?

Go supports coverage profiling for integration tests, but the flag -cover must be added when running go build: https://go.dev/doc/build-cover . Because our integration suite is containerized, and I need a container of the Go service; if I'm using Ko to build the containers, then I would like one build without -cover (i.e. for production) and one build with -cover (i.e. for integration testing).

At the moment there is no way to handle this without separate configuration files and setting KO_CONFIG_PATH for the different configuration files.