Move backup provider change warning into the backup configure dialog

dashboard/src/components/BackupDialog.vue

@@ -17,6 +17,7 @@ const config = ref({});
 const formError = ref({});
 const busy = ref(false);
 const provider = ref('');
+const oldProvider = ref('');
 const providerConfig = ref({
   limits: {},
   mountOptions: {},
@@ -157,6 +158,7 @@ defineExpose({
     config.value = result;
     formError.value = {};
     busy.value = false;
+    oldProvider.value = result.provider;
     provider.value = result.provider;
     providerConfig.value = result;
 
@@ -195,6 +197,7 @@ defineExpose({
         <fieldset :disabled="busy">
           <input style="display: none;" type="submit"/>
           <div class="error-label" v-show="formError.generic">{{ formError.generic }}</div>
+          <div class="warning-label" v-show="oldProvider !== provider">Backups in the old storage location have to be removed manually.</div>
 
           <BackupProviderForm v-model:provider="provider" v-model:provider-config="providerConfig" :form-error="formError"/>