[Observability] Update deprecated navLinks reference to use new API

[ryankeairns]

@legrego noticed that the Observability Overview page was being returned in search results and, upon further digging, @pgayvallet noticed that a deprecated API was in use. This should be updated to use App.updater$.

kibana/src/core/public/chrome/nav_links/nav_links_service.ts

Lines 76 to 82 in bf04235

	* @deprecated Uses the {@link AppBase.updater$} property when registering
	* your application with {@link ApplicationSetup.register} instead.
	*
	* @param id
	* @param values
	*/
	update(id: string, values: ChromeNavLinkUpdateableFields): ChromeNavLink | undefined;

Originally posted by @pgayvallet in #71494 (comment)

cc:/ @myasonik