title: Vuetify / DataTable: Changing style for 'show-group-by' button?
body: <p>I want to use the default grouping function in the vuetify datatable.<br />
  It works fine, but I want to change the default button style for grouping and replace it with an icon.<br />
  Is that possible? If I inspect the button in the dev tools, it just shows <code>&lt;span&gt;group&lt;/span&gt;</code>.<br />
  Found only this in the docs: <a href="https://vuetifyjs.com/en/components/data-tables/#grouped-rows" rel="nofollow noreferrer">https://vuetifyjs.com/en/components/data-tables/#grouped-rows</a></p>
  <p>Edit: By now I know what I would like. I am looking for the default template for the <code>v-slot:header</code>. This is where the button I mentioned above is generated that starts the grouping.</p>