docs: note namespace apply/delete behaviors, fix metric (#17527)

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       |