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.

cli/testdata/coder_--help.golden

@@ -43,6 +43,7 @@ SUBCOMMANDS:
                       password
     restart           Restart a workspace
     schedule          Schedule automated start and stop times for workspaces
+    secret            Manage secrets
     server            Start a Coder server
     show              Display details of a workspace's resources and agents
     speedtest         Run upload and download tests from your machine to a