* config: fix multi consul and vault config parse
Capture the loop variable when parsing multiple Consul and Vault
configuration blocks so the duration parse function uses the correct
field when it's called later on.
* client: build Vault client with right config
When setting up the multiple Vault clients, the code was always loading
the default configuration, resulting in all clients to be configured the
same way.
* config: fix WorkloadIdentityConfig.Copy() method
Ensure `WorkloadIdentityConfig.Copy()` does not return the original
pointer for the `TTL` field.
Add the plumbing we need to accept multiple Vault clusters in Nomad agent
configuration, to support upcoming Nomad Enterprise features. The `vault` blocks
are differentiated by a new `name` field, and if the `name` is omitted it
becomes the "default" Vault configuration. All blocks with the same name are
merged together, as with the existing behavior.
Unfortunately we're still using HCL1 for parsing configuration and the `Decode`
method doesn't parse multiple blocks differentiated only by a field name without
a label. So we've had to add an extra parsing pass, similar to what we've done
for HCL1 jobspecs.
For now, all existing consumers will use the "default" Vault configuration, so
there's no user-facing behavior change in this changeset other than the contents
of the agent self API.
Ref: https://github.com/hashicorp/team-nomad/issues/404
