Make api package dedicated module

As other controllers depend on source-controller because of the API
package, but this pulls in obsolete dependencies for the controllers.
By publishing the API package as a dedicated module while
using a (local) replace for the project itself, this should be
prevented.

Author: hiddeco

Dockerfile

@@ -2,6 +2,9 @@ FROM golang:1.14 as builder
 
 WORKDIR /workspace
 
+# copy api submodule
+COPY api/ api/
+
 # copy modules manifests
 COPY go.mod go.mod
 COPY go.sum go.sum
@@ -11,7 +14,6 @@ RUN go mod download
 
 # copy source code
 COPY main.go main.go
-COPY api/ api/
 COPY controllers/ controllers/
 COPY pkg/ pkg/
 COPY internal/ internal/

api/go.mod

@@ -0,0 +1,9 @@
+module github.com/fluxcd/source-controller/api
+
+go 1.14
+
+require (
+	k8s.io/api v0.18.4
+	k8s.io/apimachinery v0.18.4
+	sigs.k8s.io/controller-runtime v0.6.1
+)