Allow for multiple templates on a single page

[daviddarnes]

Is your feature request related to a problem? Please describe.
It would be great if more than one template could be used on a single page. Right now if you want to use a custom template all instances of link-peek will use the exact same template with the ID of link-peek-template.

Describe the solution you'd like
Same behaviour as before but you could override the ID that the component looks for when using a custom template. Here's a sudo code example:

<template id="my-custom-template">
  <blockquote data-key="content"></blockquote>
</template>

<link-peek api="https://api.microlink.io/?url=${link}">
  <a href="https://darn.es">David Darnes</a>
</link-peek>

Any instance without the template attribute would either use the default template within the component or, if there is one, the template with an ID of link-peek-template. This would mean there would be no breaking changes to peoples usage of the component.