New execution-Prefill doesn't prefill the Execution labels
### Explain the bug

Using the _New execution-Prefill_ is designed to easily allow starting a new execution using selected execution with modified "input set". The "set" includes both flow inputs and execution labels.

The labels are currently not prefilled. This leads to errors due to mislabeled executions.

### Environment Information

- Kestra Version: 0.12.0 as of Sep 26th 2023
- Operating System and Java Version (if not using Kestra Docker image):

ui/src/components/flows/FlowRun.vue
ui/src/components/flows/FlowRun.vue
diff --git a/ui/src/components/flows/FlowRun.vue b/ui/src/components/flows/FlowRun.vue
index a66721107d..f36eefcf1e 100644
--- a/ui/src/components/flows/FlowRun.vue
+++ b/ui/src/components/flows/FlowRun.vue
@@ -86,6 +86,7 @@
                 :label="$t('execution labels')"
             >
                 <label-input
+                    :key="executionLabels"
                     v-model:labels="executionLabels"
                 />
             </el-form-item>
@@ -196,9 +197,15 @@
                                 inputValue = JSON.stringify(inputValue).toString()
                             }
 
+                            if(inputValue === null) {
+                                inputValue = undefined;
+                            }
+
                             return [inputName, inputValue]
                         })
                 );
+                // add all labels except the one from flow to prevent duplicates
+                this.executionLabels = this.execution.labels.filter(label => !this.flow.labels.some(flowLabel => flowLabel.key === label.key && flowLabel.value === label.value));
             },
             onSubmit(formRef) {
                 if (this.$tours["guidedTour"].isRunning.value) {
