docs: add some extra documentation around client host environment var…

…iables (#11208)

Co-authored-by: Michael Schurter <mschurter@hashicorp.com>

website/content/docs/job-specification/meta.mdx

@@ -41,6 +41,8 @@ Metadata is merged up the job specification, so metadata defined at the job
 level applies to all groups and tasks within that job. Metadata defined at the
 group layer applies to all tasks within that group.
 
+Meta values are made available inside tasks as [runtime environment variables][env_meta].
+
 ## `meta` Parameters
 
 The "parameters" for the `meta` stanza can be any key-value. The keys and values
@@ -93,3 +95,4 @@ meta = {
 [group]: /docs/job-specification/group 'Nomad group Job Specification'
 [task]: /docs/job-specification/task 'Nomad task Job Specification'
 [interpolation]: /docs/runtime/interpolation 'Nomad interpolation'
+[env_meta]: /docs/runtime/environment#meta

website/content/docs/runtime/environment.mdx

@@ -105,6 +105,14 @@ Currently there is no enforcement that the meta keys be lowercase, but using
 multiple keys with the same uppercased representation will lead to undefined
 behavior.
 
+## Host environment variables
+
+Nomad passes the environment variables defined in the client host to tasks when
+using the `exec`, `raw_exec`, and `java` task drivers. The variables that are
+passed to the tasks can be controlled using the client configuration
+[`env.denylist`][].
+
 [jobspec]: /docs/job-specification 'Nomad Job Specification'
 [vault]: /docs/vault-integration 'Nomad Vault Integration'
 [filesystem internals]: /docs/internals/filesystem
+[`env.denylist`]: /docs/configuration/client#env-denylist