Extend Tramp kubernetes method

Extend Tramp kubernetes method

* doc/misc/tramp.texi (Inline methods): Adapt kubernetes method.

* etc/NEWS: Describe changes in Tramp kubernetes method.

* lisp/net/tramp-container.el (tramp-kubernetes-context)
(tramp-kubernetes-namespace): New defcustoms.
(tramp-kubernetes--completion-function): Extend for CONTAINER.POD
syntax.
(tramp-kubernetes--host-name-regexp): New defconst.
(tramp-kubernetes--container, tramp-kubernetes--pod)
(tramp-kubernetes--current-context): New defuns.
(tramp-kubernetes--current-context-data): Simplify.
(tramp-kubernetes--context-namespace): New defun.
(tramp-methods) <kubernetes>: Respect container, context and
namespace.  (Bug#59797)
(tramp-container-connection-local-default-kubernetes-variables):
New defconst.  Set respective connection-local variables.

* lisp/net/tramp-sh.el (tramp-config-check): New variable.
(tramp-open-connection-setup-interactive-shell): Use it.

* lisp/net/tramp.el (tramp-methods): Adapt docstring.
(tramp-extra-expand-args): New defvar.
(tramp-expand-args): Use it.