asdf-dotnet or asdf-dotnet-core ?

### Is your feature request related to a problem? Please describe

The asdf-plugins README mention both [asdf-dotnet](https://github.com/hensou/asdf-dotnet) and [asdf-dotnet-core](https://github.com/emersonsoares/asdf-dotnet-core) for installing the [.NET framework](https://dotnet.microsoft.com/en-us/download/dotnet) (note : [.NET Core has been renamed to .NET](https://devblogs.microsoft.com/dotnet/introducing-net-5/)).

asdf-dotnet is explicitly inspired by asdf-dotnet-core according to its README. And both plugins seems to provide the same functionalities:

```
mwrobel@l1:~/projects$ asdf list all dotnet
1.1.14
1.1.14
2.1.202
2.1.818
2.2.207
3.0.103
3.1.422
5.0.408
6.0.400
7.0.100-preview.7.22377.5
mwrobel@l1:~/projects$ asdf list all dotnet-core
1.1.14
1.1.14
2.1.202
2.2.207
2.1.818
3.0.103
3.1.422
5.0.408
6.0.400
7.0.100-preview.7.22377.5
```

From a user perspective this is confusing : should we use asdf-dotnet and asdf-dotnet-core ?

### Describe the proposed solution

Maybe the asdf-vm team should "endorse" only one of those projects and remove the other ?

### Describe similar `asdf` features and why they are not sufficient

N/A

### Describe other workarounds you've considered

The "language" column in the asdf-plugins repository README could also be updated to clarify the situation.

Read the asdf-plugins README and the linked asdf-dotnet and asdf-dotnet-core READMEs first, then compare their stated scope and current version lists. Done means resolving which plugin the repository should recommend, or clearly documenting why both remain, including the README's language-column clarification.

Written by the indexing model from the issue text.