DBSCAN from Clustering.jl not registered

[juliohm]

The latest version of Clustering.jl provides DBSCAN, and yet we can't @load DBSCAN pkg=Clustering.

Reference: https://juliastats.org/Clustering.jl/stable/dbscan.html

[ablaom]

Sounds like a good idea.

PR welcome. Code goes here. The existing clusterers can be viewed as templates. I guess we only need only implement predict and not transform in this case.