Use OcSpinner as loading spinner in OcSelect

[dschmidt]

I'm not sure this is desirable after all, but I just had the idea and played around with it and would like to put it up for discussion:

vue-select has a slot for customizing the loading animation, maybe it would be cool to use our own spinner there by default instead of the vue-select one ... we have one already and it we could possibly unify the look even more 🤷🏻

The documentation is a little sparse (https://vue-select.org/guide/ajax.html#loading-spinner) but I could make it work like this:

<template v-slot:spinner="{ loading }">
  <oc-spinner v-show="loading" aria-label="Loading" size="medium"/>
</template>

The only issue is that the animation is wobbling. My CSS foo is not strong, but I assume it should be rather easy to fix :)

[dschmidt]

Fixed in #1521