feat: add customizable upgrade message on client/server version mismatch (#11587)

cli/testdata/coder_server_--help.golden

@@ -65,6 +65,11 @@ CLIENT OPTIONS:
 These options change the behavior of how clients interact with the Coder.
 Clients include the coder cli, vs code extension, and the web UI.
 
+      --cli-upgrade-message string, $CODER_CLI_UPGRADE_MESSAGE
+          The upgrade message to display to users when a client/server mismatch
+          is detected. By default it instructs users to update using 'curl -L
+          https://coder.com/install.sh | sh'.
+
       --ssh-config-options string-array, $CODER_SSH_CONFIG_OPTIONS
           These SSH config options will override the default SSH config options.
           Provide options in "key=value" or "key value" format separated by

cli/testdata/server-config.yaml.golden

@@ -433,6 +433,11 @@ client:
   # incorrectly can break SSH to your deployment, use cautiously.
   # (default: <unset>, type: string-array)
   sshConfigOptions: []
+  # The upgrade message to display to users when a client/server mismatch is
+  # detected. By default it instructs users to update using 'curl -L
+  # https://coder.com/install.sh | sh'.
+  # (default: <unset>, type: string)
+  cliUpgradeMessage: ""
   # The renderer to use when opening a web terminal. Valid values are 'canvas',
   # 'webgl', or 'dom'.
   # (default: canvas, type: string)