[REQUEST] Create a lts.json for external users to access all the LTS version details

**Is your feature request related to a problem? Please describe.**
I was developing a tool that requires knowing what are current ember LTS versions. As I searched around I couldn't find any such resources other than [lts](https://emberjs.com/releases/lts/) page on the website.
I found there will be more cases if we can provide such files and it will be easy to maintain and access.

**Describe the solution you'd like**
Currently we hard code the LTS details in the controller itself [here](https://github.com/ember-learn/ember-website/blob/283c73dc33ad8334421cef93180900fdf3c9021e/app/controllers/releases/lts.js#L3).

We should provide a `lts.json`, that will have all the information we display on `lts` page of the website and this will help if anyone wants to access it.
Sample
```
[
{
version: '4.4',
promotionDate: 'July 13, 2022',
},
{
version: '3.28',
promotionDate: December 20, 2021,
},
]
```

**Describe alternatives you've considered**
Alternatively or long-term solution I would like to have a library called `ember-lts-versions` something like [node-lts-versions](https://github.com/msimerson/node-lts-versions)