docs: note namespace apply/delete behaviors, fix metric

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

command/namespace_apply.go

@@ -34,7 +34,9 @@ Usage: nomad namespace apply [options] <input>
   Instead of a file, you may instead pass the namespace name to create
   or update as the only argument.
 
-  If ACLs are enabled, this command requires a management ACL token.
+  If ACLs are enabled, this command requires a management ACL token. In
+  federated clusters, the namespace will be created in the authoritative region
+  and will be replicated to all federated regions.
 
 General Options:
 

command/namespace_delete.go

@@ -22,6 +22,10 @@ Usage: nomad namespace delete [options] <namespace>
 
   If ACLs are enabled, this command requires a management ACL token.
 
+  You cannot delete a namespace that has non-terminal jobs. In federated
+  clusters, you cannot delete a namespace that has non-terminal jobs in any of
+  the federated regions.
+
 General Options:
 
   ` + generalOptionsUsage(usageOptsDefault|usageOptsNoNamespace)

website/content/docs/commands/namespace/apply.mdx

@@ -25,7 +25,9 @@ expected.
 Instead of a file, you may instead pass the namespace name to create
 or update as the only argument.
 
-If ACLs are enabled, this command requires a management ACL token.
+If ACLs are enabled, this command requires a management ACL token. In federated
+clusters, the namespace will be created in the authoritative region and will be
+replicated to all federated regions.
 
 ## General Options
 

website/content/docs/commands/namespace/delete.mdx

@@ -22,6 +22,10 @@ The `namespace delete` command requires the name of the namespace to be deleted.
 
 If ACLs are enabled, this command requires a management ACL token.
 
+You cannot delete a namespace that has non-terminal jobs. In federated clusters,
+you cannot delete a namespace that has non-terminal jobs in any of the federated
+regions.
+
 ## General Options
 
 @include 'general_options_no_namespace.mdx'

website/content/docs/operations/metrics-reference.mdx

@@ -154,7 +154,7 @@ Nomad will emit [tagged metrics][tagged-metrics], in the below format:
 | --------------------------------------- | ----------------------------------------------------------------------------------- | ---------- | ----- | ------------------------------------------------------------------------------------- |
 | `nomad.client.allocated.cpu`            | Total amount of CPU shares the scheduler has allocated to tasks                     | Mhz        | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |
 | `nomad.client.allocated.memory`         | Total amount of memory the scheduler has allocated to tasks                         | Megabytes  | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |
-| `nomad.client.allocated_disk`           | Total amount of disk space the scheduler has allocated to tasks                     | Megabytes  | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |
+| `nomad.client.allocated.disk`           | Total amount of disk space the scheduler has allocated to tasks                     | Megabytes  | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |
 | `nomad.client.allocations.blocked`      | Number of allocations waiting for previous versions to exit                         | Integer    | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |
 | `nomad.client.allocations.migrating`    | Number of allocations migrating data from previous versions (see [`sticky`][sticky])| Integer    | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |
 | `nomad.client.allocations.pending`      | Number of allocations pending (received by the client but not yet running)          | Integer    | Gauge | datacenter, host, node_class, node_id, node_scheduling_eligibility, node_status       |