Consider adding Julia community registry

[abelsiqueira]

Since Julia 1.0, public packages are registered in https://github.com/JuliaRegistries /General, by creating some files under LETTER/PACKAGENAME. For instance, the package NLPModels.jl is registered because there are files under https://github.com/JuliaRegistries/General/blob/master/N/NLPModels/.

All packages need an OSI-approved license to be registered in the default registry.

One check can be to verify that Package.toml exists in that folder.

[jspaaks]

Hi Abel, my initial thoughts are that we should stick to a similar mechanism as most of the other tests we have now (i.e. regex on the README) for the time being. If we do go through with the refactor into plugin architecture (#334), I anticipate that the implementation of any given test will be hidden away in a separate libray so those libraries can do whatever they think is useful for their use case.