Add sync_cursor to Sync job index mapping (#158638)

# Part of https://github.com/elastic/enterprise-search-team/issues/4665

## Summary

This PR adds a new field `sync_cursor` to index
`.elastic-connectors-sync-jobs`.


### Checklist

Delete any items that are not applicable to this PR.

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/plugins/enterprise_search/server/index_management/setup_indices.test.ts

@@ -209,6 +209,7 @@ describe('Setup Indices', () => {
             },
           },
           service_type: { type: 'keyword' },
+          sync_cursor: { type: 'object' },
         },
       },
       created_at: { type: 'date' },

x-pack/plugins/enterprise_search/server/index_management/setup_indices.ts

@@ -233,6 +233,7 @@ const indices: IndexDefinition[] = [
               },
             },
             service_type: { type: 'keyword' },
+            sync_cursor: { type: 'object' },
           },
         },
         created_at: { type: 'date' },