internal/cloudapi: expose custom repos

Expose the custom repository customizations for
the cloudapi.

internal/cloudapi/v2/v2_test.go

@@ -920,6 +920,14 @@ func TestComposeCustomizations(t *testing.T) {
 				"ignore_ssl": false,
 				"gpg_key": "some-gpg-key"
 			}],
+			"custom_repositories": [{
+				"name": "hello", 
+				"id": "hello", 
+				"baseurl": [ "http://hello.com" ],
+				"gpg_key": [ "somekey" ],
+				"check_gpg": true,
+				"enabled": true
+			}],
 			"services": {
 				"enabled": [
 					"nftables"