Support Graphs.jl's generators for common graphs

[mroavi]

Graphs.jl provides these generators for common graphs.

As far as I can tell, these cannot be used conveniently with MetaGraphsNext.jl yet:

julia> MetaGraphsNext.MetaGraph(path_graph(5), default_weight = 3.0)

 Warning: Constructing a MetaGraph with a nonempty underlying graph is not advised.
└ @ MetaGraphsNext ~/.julia/dev/MetaGraphsNext/src/metagraph.jl:55
Meta graph based on a {5, 4} undirected simple Int64 graph with vertex labels of type Symbol, vertex metadata of type Nothing, edge metadata of type Nothing, graph metadata given by nothing, and default weight 3.0

Would be nice to add support for these.

[gdalle]

The issue with this is that when building a MetaGraph with a non-empty graph, you also need to provide all the metadata and vertex labels upfront. By default metadata types for vertices and edges are Nothing, so there is an obvious value to pick if the user doesn't specify it. It gets a bit tricker with vertex labels since they must be unique.

I think #6 is part of the solution

[gdalle]

Related to #37

[gdalle]

Solved by the new bulk constructor in #45