Fix BreadcrumbAppendExtension in solution nav

[Dosant]

While working on #201596 I noticed that BreadcrumbAppendExtension just isn't there in solution nav. The BreadcrumbAppendExtension is used to append some UI next to the last breadcrumb.

kibana/src/core/packages/chrome/browser/src/contracts.ts

Lines 93 to 103 in 64b6a1a

	/**
	* Get an observable of the current extension appended to breadcrumbs
	*/
	getBreadcrumbsAppendExtension$(): Observable<ChromeBreadcrumbsAppendExtension | undefined>;
	/**
	* Mount an element next to the last breadcrumb
	*/
	setBreadcrumbsAppendExtension(
	breadcrumbsAppendExtension?: ChromeBreadcrumbsAppendExtension
	): void;

We need to add it solution nav to make #201596 work properly.

This also means there is now missing functionality in solution nav

• Search sessions indicator won't appear (this is fine because the feature is deprecated, but worth fixing) cc @elastic/kibana-data-discovery
• Logs explorer feedback link won't appear

  kibana/x-pack/solutions/observability/plugins/observability_logs_explorer/public/components/logs_explorer_top_nav_menu.tsx

  Lines 103 to 117 in 8902f70

  	chrome.setBreadcrumbsAppendExtension({
  	content: toMountPoint(
  	<EuiHeaderSection
  	data-test-subj="logsExplorerHeaderMenu"
  	css={css`
  	margin-left: ${euiTheme.size.m};
  	`}
  	>
  	<EuiHeaderSectionItem>
  	<FeedbackLink />
  	</EuiHeaderSectionItem>
  	</EuiHeaderSection>,
  	{ theme, i18n: i18nStart }
  	),
  	});

  . Not sure how ciritical is that cc @elastic/obs-ux-logs-team
• I haven't found any other usages

We also should improve the API to properly support multiple slots to avoid workarounds like:

kibana/x-pack/solutions/observability/plugins/observability_logs_explorer/public/components/logs_explorer_top_nav_menu.tsx

Lines 91 to 99 in 8902f70

	/**
	* Since the breadcrumbsAppendExtension might be set only during a plugin start (e.g. search session)
	* we retrieve the latest valid extension in order to restore it once we unmount the beta badge.
	*/
	const [previousAppendExtension$] = useState(() =>
	chrome.getBreadcrumbsAppendExtension$().pipe(filter(Boolean), take(1))
	);
	const previousAppendExtension = useObservable(previousAppendExtension$);

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)