[FEATURE-REQUEST] custom html tag for show/edit page

**Describe the problem you're proposing to solve**
Since the show and edit are on the same page it would be good to be able to put custom HTML tags that aren't submitted as well. For example, there is no easy way to display a big image on the show/edit page. I know that this can be done via custom Ecto type but in my case, I already have a custom Ecto type from my upload lib (Arc/Waffle). Also, I'm not a fan of adding an admin logic code to the application code.

**Describe the solution you'd like**
be able to add custom html tags to show/edit form so something like:
```
def form_fields(_) do
[
status: %{choices: [{"Valid", "valid"}, {"New", "new"}, {"Invalid", "invalid"}]},
id_card_front: %{name: "ID Front", type: :safe_html, value: fn v -> "