embed_bqm should accept an edge list for it's target graph in addition to adj

[arcondello]

Current Problem A common format for graphs is an edgelist and we can support that with embed_bqm, embed_ising and embed_qubo.

Proposed Solution It would be nice if we could provide an edgelist so

emb = embed_bqm(bqm, embedding, [(0, 1), (1, 2)])

would work