Add structs and fields to support the Nomad Pools Governance Enterprise
feature of controlling node pool access via namespaces.
Nomad Enterprise allows users to specify a default node pool to be used
by jobs that don't specify one. In order to accomplish this, it's
necessary to distinguish between a job that explicitly uses the
`default` node pool and one that did not specify any.
If the `default` node pool is set during job canonicalization it's
impossible to do this, so this commit allows a job to have an empty node
pool value during registration but sets to `default` at the admission
controller mutator.
In order to guarantee state consistency the state store validates that
the job node pool is set and exists before inserting it.
This changeset includes some fixes to documentation discovered while working on
node pools, but we didn't want to include in the node pool PRs so they can get
backported easily:
* namespace apply/delete commands are forwarded to the authoritative region
* deleting a namespace requires there are no non-terminal jobs in any of the
federated regions
* fixed a typo in the name of the `nomad.client.allocated.disk` metric
The new `namespace apply` feature that allows for passing a namespace
specification file detects the difference between an empty namespace
and a namespace specification by checking if the file exists. For most
cases, the file will have an extension like `.hcl` and so there's
little danger that a user will apply a file spec when they intended to
apply a file name.
But because directory names typically don't include an extension,
you're much more likely to collide when trying to `namespace apply` by
name only, and then you get a confusing error message of the form:
Failed to read file: read $namespace: is a directory
Detect the case where the namespace name collides with a directory in
the current working directory, and skip trying to load the directory.
