Enable challenges to be closed by "End Challenge" button fix#11339 (#11342)

* fix the dropdown list empty problem in close-challenge-modal

* fix the memberSearchDropdown not accepting input problem

* prevent submit event in dropdown input reloading the page

website/client/components/members/memberSearchDropdown.vue

@@ -1,6 +1,6 @@
 <template lang="pug">
 b-dropdown.create-dropdown(:text="text", no-flip)
-  b-dropdown-form(:disabled='true')
+  b-dropdown-form(:disabled='false', v-on:submit.prevent="onSubmit")
     input.form-control(type='text', v-model='searchTerm')
   b-dropdown-item(v-for="member in memberResults", :key="member._id", @click="selectMember(member)")
     | {{ member.profile.name }}

website/client/mixins/challengeMemberSearch.js

@@ -6,8 +6,11 @@ export default {
     searchTerm: debounce(function searchTerm (newSearch) {
       this.challengeMemberSearchMixin_searchChallengeMember(newSearch);
     }, 500),
-    members () {
-      this.memberResults = this.members;
+    members: {
+      handler () {
+        this.memberResults = this.members;
+      },
+      immediate: true,
     },
   },
   methods: {