worker: allow passing different jobs to workers

Until now, all jobs were put as "osbuild" jobs into the job queue and
the worker API hard-coded sending an osbuild manifest and upload
targets.

Change the API to take a "type" and "args" keys, which are equivalent to
the job-queue's type and args. Workers continue to support only osbuild
jobs, but this makes other jobs possible in the future.

internal/worker/server_test.go

@@ -68,7 +68,7 @@ func TestCreate(t *testing.T) {
 	require.NoError(t, err)
 
 	test.TestRoute(t, server, false, "POST", "/jobs", `{}`, http.StatusCreated,
-		`{"manifest":{"sources":{},"pipeline":{}}}`, "id", "location", "artifact_location")
+		`{"type":"osbuild","args":{"manifest":{"pipeline":{},"sources":{}}}}`, "id", "location", "artifact_location")
 }
 
 func TestCancel(t *testing.T) {