feat: add CLI support for user secrets (#24270)

Adds a coder secret command group for managing user secrets from the
CLI, with create, update, list, and delete subcommands backed by the
existing user secret API.

This branch adds CLI test coverage and refreshes the generated help
output and CLI reference docs for the new command group.

docs/manifest.json

@@ -2016,6 +2016,31 @@
 							"description": "Edit workspace stop schedule",
 							"path": "reference/cli/schedule_stop.md"
 						},
+						{
+							"title": "secret",
+							"description": "Manage secrets",
+							"path": "reference/cli/secret.md"
+						},
+						{
+							"title": "secret create",
+							"description": "Create a secret",
+							"path": "reference/cli/secret_create.md"
+						},
+						{
+							"title": "secret update",
+							"description": "Update a secret",
+							"path": "reference/cli/secret_update.md"
+						},
+						{
+							"title": "secret list",
+							"description": "List secrets, or show one by name",
+							"path": "reference/cli/secret_list.md"
+						},
+						{
+							"title": "secret delete",
+							"description": "Delete a secret",
+							"path": "reference/cli/secret_delete.md"
+						},
 						{
 							"title": "server",
 							"description": "Start a Coder server",