rcm: rework the API for submitting composes

The API allowed composes to have multiple architectures, image
types and repositories. Turns out that's not exactly what we want
it is not clear how to combine the lits of each. Each architecture
might not combine with each image type, and it is not clear which
repositories are need for each image build. Lastly, while allowing
different image builds to have different distros in the same
compose does not appear immediately useful, there is no particular
reason to disallow that. This patch reworks the way composes are
specified.

The intention remains the same, to be able to submit several image
builds as one compose. But rather than taking arrays of image types
and architectures, take one array of image builds instead, each of
which consists of one distro, one architecture, one image build and
an array of repositories.

In a follow-up patch they will also each contain an array of upload
targets.

This means that each image build will have the same sort of structure
as a compose request in the weldr API. The reason we want to submit
an array of them rather than have them as individual composes, is that
in a follow-up patch we will introduce the concept of a "finalizer",
or "call-back" or something to that effect, which will be triggered
when all the images have been built successfully. The use-case is,
as always, koji, which requires this.

Signed-off-by: Tom Gundersen <teg@jklm.no>

cmd/osbuild-rcm-tests/main_test.go

@@ -7,22 +7,31 @@ package main
 
 import (
 	"encoding/json"
-	"github.com/google/uuid"
-	"github.com/stretchr/testify/require"
 	"net/http"
 	"strings"
 	"testing"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/require"
 )
 
 func TestRCM(t *testing.T) {
 	// This is the first request the user sends to osbuild.
 	submitBody := `
 		{
-			"distribution": "fedora-31",
-		 	"image_types": ["qcow2"], 
- 		 	"architectures":["x86_64"], 
-			"repositories": [
-				{"url": "http://download.fedoraproject.org/pub/fedora/linux/releases/30/Everything/x86_64/os/"}
+			"image_builds":
+			[
+				{
+					"distribution": "fedora-31",
+					"architecture": "x86_64",
+					"image_type": "qcow2",
+					"repositories":
+					[
+						{
+							"baseurl": "http://download.fedoraproject.org/pub/fedora/linux/releases/30/Everything/x86_64/os/"
+						}
+					]
+				}
 			]
 		}
 	`