[Observability] Wraps render tree with KibanaThemeProvider

[claudiopro]

Summary

This PR wraps render trees of Observability apps into KibanaThemeProvider as requested by #118866. It also adds options containing the value of theme$ as second argument of toRenderMount, passing it down from AppMountParams.

Closes #120896.

Checklist

Delete any items that are not applicable to this PR.

• Unit or functional tests were updated or added to match the most common scenarios
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)

[fkanout]

@claudiopro would you please link the PR with the issue? I was going to pick it up 😄 .e.g use the fix keyword OR link it from the UI(right side panel).

[claudiopro]

Sure! I haven't heard from @estermv who owns #119499 to avoid overlapping, so I'll go ahead and create a new issue for Actionable Observability.

[claudiopro]

I'm not sure whether this occurrence belongs to us:

kibana/x-pack/plugins/observability/public/components/shared/header_menu_portal.tsx

Lines 13 to 21 in a00fa53

	// eslint-disable-next-line import/no-default-export
	export default function HeaderMenuPortal({ children, setHeaderActionMenu }: HeaderMenuPortalProps) {
	const portalNode = useMemo(() => createPortalNode(), []);
	useEffect(() => {
	setHeaderActionMenu((element) => {
	const mount = toMountPoint(<OutPortal node={portalNode} />);
	return mount(element);
	});

[justinkambic]

Uptime change LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 4029b2f
• Storybooks Preview

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
observability	362.6KB	362.7KB	+126.0B

History

• 💚 Build #11240 succeeded 3249543
• 💚 Build #11083 succeeded d7ff330

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream