distroless: rewrite docker-entrypoint.sh in go

See go doc ./cmd/docker-entrypoint for why.

Signed-off-by: Andrew Keesler <akeesler@vmware.com>

Makefile

@@ -48,6 +48,7 @@ bin/example-app:
 .PHONY: release-binary
 release-binary: generate
 	@go build -o /go/bin/dex -v -ldflags $(LD_FLAGS) $(REPO_PATH)/cmd/dex
+	@go build -o /go/bin/docker-entrypoint -v -ldflags $(LD_FLAGS) $(REPO_PATH)/cmd/docker-entrypoint
 
 docker-compose.override.yaml:
 	cp docker-compose.override.yaml.dist docker-compose.override.yaml