optionally return node metadata in NodeListStub

### Proposal

Currently NodeListStub doesn't contain the node metadata. If you want to get that you have to get the full node information.
Propose that NodeStubFields be extended to include "Meta", and if included, populate metadata in the response.

Is there any reason not to include that? Is done deliberately for security reasons for example?

### Use-cases

We're migrating from using information provided through the driver to using the dynamic node metadata. NodeListStub contains the driver attributes, but it doesn't contain the node metadata.

### Attempted Solutions

Alternative is that having listed the nodes, have to list through and get the full node information for each node just to get the metadata. This will be inefficient for a large number of nodes.

On the face of it this wouldn't appear to be a very complicated change, and I'm happy to try and give it a go if it's likely that a PR along these lines would be accepted. There may be things I'm not aware of though that would prevent it.

Start by locating NodeListStub and NodeStubFields in the Nomad codebase, then trace how node-list responses select and populate fields. Confirm how the existing full node response exposes metadata and define completion as optionally returning Meta in node-list responses without requiring separate full-node lookups.

Written by the indexing model from the issue text.