Use Contextual Component pattern to yield multiple blocks in Hero

Right now the `docs-hero` component assumes that the only use-case for using it in block form is to pass in a custom logo. However, users may want to render additional content in the Hero template, such as a set of badges. It would be great to allow multiple yields similar to the following pattern:

```
{{#docs-hero as |hero|}}
{{#hero.top}}
{{/hero.top}}

{{#hero.bottom}}
{{/hero.bottom}}
{{/docs-hero}}
```

An example of how a developer might want to use this:

Locate the docs-hero component and its Hero template, then inspect how block content and the existing custom-logo use case are handled. The work is complete when callers can provide multiple named blocks such as hero.top and hero.bottom while preserving the current block behavior.

Written by the indexing model from the issue text.