Add support for using MemPool with DistributedNext.jl

[JamesWrigley]

This won't work until registration finishes: JuliaRegistries/General#120499

But in the meantime you can add this to Project.toml:

[sources]
DistributedNext = {url="https://github.com/JuliaParallel/DistributedNext.jl.git"}

[jpsamaroo]

❤️

[jpsamaroo]

Thanks a bunch!