Problem: we need a extract metadata for nodes and then parse into a cluster graph
Solution: create a compspec create nodes subcommand.

In this PR I am adding a ClusterGraph, which still needs work to improve the output
to easily map into a JGF (right now it has elements that can support any type
that need further parsing). I am also generalizing the idea of plugins more, so
we will have extractors and converters (that run create) but I need to finalize
the design for the latter, right now the create commands are very separate. I
am opening the PR sooner than later in case my computer explodes. A few problems
I have run into is that NFD does not have cpu counts, let along physical vs.
logical. This information is in /proc/cpuinfo for x86 but not arm. We also
do not have a way to get socket -> core mapping. So likely we do need to add
the hwloc extractor, and provide an automated build for doing that since
it requires hwloc on the system. I will put some thought into this.

Signed-off-by: vsoch <[email protected]>

Problem: we did not have a way to define a creator as a plugin.
Solution: add a plugin interface to create. I originally was going
to create separate plugin types, but I like the idea that one plugin
family can decide to define both easily. When this is refactored to
have a more "register" design (to make it flexible to changing the set
available) it will be nice to provide Create/Extract from the same
interface and keep the number of interfaces / functions for them
minimal. I was going to add hwloc now, but there seems to be a
bug so we will need to move forward prototyping with the current
proxy for nodes, which is just using the go runtime package. We
obviously need to improve upon this.

Signed-off-by: vsoch <[email protected]>