Add start-for-ten fetch service

This gives an initial starting example for how we can grab the data we need for the view without needing to make a request to the legacy service or parse its response.

app/services/return-logs/fetch-return-log.service.js

@@ -0,0 +1,28 @@
+'use strict'
+
+const ReturnLogModel = require('../../../app/models/return-log.model.js')
+
+/**
+ * Fetch the selected return log and all associated data needed for the view
+ *
+ * @param {string} returnId - The return log ID
+ *
+ * @returns {Promise<module:ReturnLogModel>} the matching `ReturnLogModel` instance
+ */
+async function go(returnId) {
+  return _fetch(returnId)
+}
+
+async function _fetch(returnId) {
+  return ReturnLogModel.query()
+    .findById(returnId)
+    .withGraphFetched('licence')
+    .withGraphFetched('returnSubmissions')
+    .modifyGraph('returnSubmissions', (returnSubmissionsBuilder) => {
+      returnSubmissionsBuilder.orderBy('version', 'desc').limit(1).withGraphFetched('returnSubmissionLines')
+    })
+}
+
+module.exports = {
+  go
+}