feat: implement a shared Glitch shortcode

[mamieorine]

Resolves #64

The Glitch shortcode on both d.d.c and web.dev have the same design and code structure. So, this shortcode can be moved into webdev-infra so it will be a shared shortcode which can be used by both d.c.c and web.dev.

Changes in this pull request:

• Adds a new shared Glitch shortcode

Usages:

{% Glitch {
  id: 'tabindex-zero',
  path: 'index.html',
  previewSize: 0,
  allow: []
} %}

{% Glitch 'tabindex-zero' %}

[mamieorine]

@matthiasrohmer I have tested a shared Glitch shortcode with web.dev and d.c.c, it works fine with both site.

The results of testing a shortcode with both web.dev and d.c.c. are shown below:

• web.dev
• d.c.c.