Handle amend lesson mutation like other use sites & add it to props

aleksis/apps/chronos/frontend/components/amendLesson.graphql

-mutation gqlAmendLesson($input: LessonEventInput!) {
+mutation createAmendLesson($input: LessonEventInput!) {
   amendLesson(input: $input) {
     lessonEvent {
       id

aleksis/apps/chronos/frontend/components/calendar_feeds/details/LessonDetails.vue

@@ -106,7 +106,7 @@
         :default-item="amendEvent.default"
         :is-create="true"
         createItemI18nKey="chronos.event.amend.title"
-        :gql-create-mutation="gqlAmendLesson"
+        :gql-create-mutation="amendEvent.gqlCreateMutation"
         @cancel="amendEvent.open = false"
       />
       </v-card-actions>
@@ -126,7 +126,7 @@ import LessonRelatedObjectChip from "../../LessonRelatedObjectChip.vue";
 
 import lessonEvent from "../mixins/lessonEvent";
 import LessonEventSubject from "../../LessonEventSubject.vue";
-import gqlAmendLesson from "../../amendLesson.graphql";
+import createAmendLesson from "../../amendLesson.graphql";
 
 export default {
   name: "LessonDetails",
@@ -138,7 +138,6 @@ export default {
     CancelledCalendarStatusChip,
     EditButton,
     DialogObjectForm,
-    gqlAmendLesson,
   },
   mixins: [calendarFeedDetailsMixin, lessonEvent],
   data() {
@@ -174,6 +173,7 @@ export default {
           cancelled: false,
           comment: ""
         },
+        gqlCreateMutation: createAmendLesson,
       },
     };
   },