docs: clarify consumers of environment variables for CLI (#26459)

In https://github.com/hashicorp/nomad/issues/15459 we've had a bit of
back-and-forth as a result of applying Nomad environment variables where they
typically should not be used. Clarify that the env vars are for the CLI and
mostly not for the agent. Also move the `NOMAD_CLI_SHOW_HINTS` description into
the correct section.

website/content/commands/index.mdx

@@ -60,7 +60,9 @@ the [`tls` block in agent configuration] for details.
 ### Environment variables
 
 Nomad can use environment variables to configure command-line tool options. You
-may override these environment variables with individual flags.
+may override these environment variables with individual flags. Except where
+noted, these variables influence the behavior of the Nomad CLI and should not be
+set for Nomad agents.
 
 #### Connection environment variables
 
@@ -89,10 +91,10 @@ may override these environment variables with individual flags.
 
 - `NOMAD_CLI_NO_COLOR` - Disables colored command output.
 
-#### Mutual TLS (mTLS) environment variables
-
 - `NOMAD_CLI_SHOW_HINTS` - Enables ui-hints in common CLI command output.
 
+#### Mutual TLS (mTLS) environment variables
+
 - `NOMAD_CLIENT_CERT` - Path to a PEM encoded client certificate for TLS
   authentication to the Nomad server. Must also specify `NOMAD_CLIENT_KEY`.
 
@@ -114,6 +116,10 @@ may override these environment variables with individual flags.
 
 #### Nomad Enterprise license environment variables
 
+These environment variables influence the Nomad Enterprise license
+configuration. These values are only used for Nomad Enterprise agents, not the
+Nomad CLI.
+
 - `NOMAD_LICENSE_PATH` - An absolute path to a Nomad Enterprise license file,
   for example `/etc/nomad.d/license.hclic`.