This update adds a ✨ _new_ `<PostList />` component, along with it's child components (`<PostListItem/>` and `<PostListItemDetails />`). This new generic component can be used to show a list of posts.
It can be used like so:
```js
/**
* A component that renders a list of posts
*
* @component PostList
*
* @args {Array<Object>} posts - The array of post objects to display
* @args {Function} fetchMorePosts - A function that fetches more posts. Must return a Promise that resolves to an array of new posts.
* @args {String} emptyText (optional) - Custom text to display when there are no posts
* @args {String|Array} additionalItemClasses (optional) - Additional classes to add to each post list item
* @args {String} titleAriaLabel (optional) - Custom Aria label for the post title
*
*/
```
```hbs
<PostList
@posts={{this.posts}}
@fetchMorePosts={{this.loadMorePosts}}
@emptyText={{i18n "custom_identifier.empty"}}
@additionalItemClasses="custom-class"
/>
```
* FIX: respect creation date when paginating group activity posts
There are scenarios where the chronological order of posts doesn't match the order of their IDs. For instance, when moving the first post from one topic or PM to another, a new post (with a higher ID) will be created, but it will retain the original creation time.
This PR changes the group activity page and endpoint to paginate posts using created_at instead of relying on ID ordering.
