Let Tramp sudo sessions expire after a timeout

Let Tramp sudo sessions expire after a timeout

* doc/misc/tramp.texi (Inline methods) <sudo, doas>: Both methods expire
the underlying session per default.
(Predefined connection information): Explain "session-timeout".

* etc/NEWS: Mention Tramp session expiration.

* lisp/net/tramp-sh.el (tramp-methods) <sudo, doas>:
Add `tramp-session-timeout'.
(tramp-timeout-session): New defun.
(tramp-maybe-open-connection): Handle session timeout.

* lisp/net/tramp.el (tramp-methods): Adapt docstring.
(tramp-equal-remote): Extend.