Run newsticker's ticker only periodically (bug#59856)

Run newsticker's ticker only periodically (bug#59856)

* doc/misc/newsticker.texi (Frontends, Configuration): Add
newsticker-ticker-period
* lisp/net/newst-ticker.el (newsticker--ticker-period-timer): New.
(newsticker--ticker-timer): Modify doc string.
(newsticker-ticker-interval): Modify doc string.
(newsticker-ticker-period): New
(newsticker--display-tick, newsticker--display-jump)
(newsticker--display-scroll, newsticker-start-ticker)
(newsticker-stop-ticker): Use newsticker--ticker-timer and
newsticker--ticker-period-timer.