Add option to link an external registration provider for events

js/src/components/Event/ExternalParticipationButton.vue

@@ -0,0 +1,27 @@
+<template>
+  <div class="participation-button">
+    <a
+      class="button is-large is-primary"
+      type="button"
+      target="_blank"
+      :href="
+        event.externalParticipationUrl
+          ? encodeURI(`${event.externalParticipationUrl}?uuid=${event.uuid}`)
+          : '#'
+      "
+      :disabled="!event.externalParticipationUrl"
+      >{{ $t("Go to booking") }}&nbsp;
+      <b-icon style="margin-left: 0" icon="open-in-new"
+    /></a>
+  </div>
+</template>
+
+<script lang="ts">
+import { Component, Prop, Vue } from "vue-property-decorator";
+import { IEvent } from "../../types/event.model";
+
+@Component
+export default class ExternalParticipationButton extends Vue {
+  @Prop({ required: true }) event!: IEvent;
+}
+</script>