REGTESTS: cli: add a smoke test for the read-only CLI commands

REGTESTS: cli: add a smoke test for the read-only CLI commands

Most of the "show" commands of the CLI had no coverage at all, so a
crash or a broken output in one of their dump functions would go
unnoticed. This test issues show version, cli level, cli sockets, env,
startup-logs, dev, backend, defaults, default-server, servers state,
servers conn, stat, info, schema json, sess, errors, fd, pools,
activity, threads, tasks, profiling, anon, table, map and acl once on a
small but non-empty configuration.

The patterns are deliberately loose: the point is to verify that each
command is accepted and that its dump reaches its first line, not to
freeze output formats which are explicitly allowed to change.