[FEATURE] Code Injection

[vlavrynovych]

Is your feature request related to a problem? Please describe.
I am using the Ghost as a blogging platform and it has a code injection feature which helps me as an owner of my blog to tune it where needed like styles, integrations, new functionality, etc.

Describe the solution you'd like
I wish to have a dedicated section for the snippets which I publicly share (or collections, see my comment from #49). New button will open a window with a textarea component where I will be ablt to inject any HTML content like this:

<script>
... my scripts
</script>
<style>
.. my styles
</style>

Ideally if it's possible to allow to inject this code to the header and footer as a separate areas.

Additional context
I can share the link to the Ghost doc of the same feature.

Priority
⬇️ The priority for this request is super low