Added form footer actions component

app/assets/javascripts/vue_shared/components/form/form_footer_actions.vue

+<template functional>
+  <footer class="form-actions d-flex justify-content-between">
+    <div><slot name="prepend"></slot></div>
+    <div><slot></slot></div>
+    <div><slot name="append"></slot></div>
+  </footer>
+</template>

spec/frontend/vue_shared/components/form/form_footer_actions_spec.js

+import FormFooterActions from '~/vue_shared/components/form/form_footer_actions.vue';
+import { shallowMount } from '@vue/test-utils';
+
+describe('Form Footer Actions', () => {
+  let wrapper;
+
+  function createComponent(slots = {}) {
+    wrapper = shallowMount(FormFooterActions, {
+      slots,
+    });
+  }
+
+  afterEach(() => {
+    wrapper.destroy();
+  });
+
+  it('renders content properly', () => {
+    const defaultSlot = 'Foo';
+    const prepend = 'Bar';
+    const append = 'Abrakadabra';
+    createComponent({
+      default: defaultSlot,
+      prepend,
+      append,
+    });
+
+    expect(wrapper.text().replace(/\s+/g, '')).toBe(`${prepend}${defaultSlot}${append}`);
+  });
+});