feat: add copilot window for stats

[caalador]

Add a copilot window to look at
collected stats.

To see window in any mode but play
click on the bar-graph observability
button.

[heruan]

This duplicates almost verbatim this ensureClientLoaded method:

observability-kit/observability-kit-micrometer/src/main/java/com/vaadin/observability/micrometer/client/MetricsCollectorElement.java

Lines 78 to 99 in b057a03

	private static void ensureClientLoaded(UI ui) {
	if (ComponentUtil.getData(ui, CLIENT_INIT_KEY) != null) {
	return;
	}
	ComponentUtil.setData(ui, CLIENT_INIT_KEY, Boolean.TRUE);
	ClassLoader loader = MetricsCollectorElement.class.getClassLoader();
	try (InputStream in = loader.getResourceAsStream(CLIENT_RESOURCE)) {
	if (in == null) {
	LoggerFactory.getLogger(MetricsCollectorElement.class).warn(
	"observability-kit client resource not found: {}",
	CLIENT_RESOURCE);
	return;
	}
	String js = StringUtil.removeComments(
	new String(in.readAllBytes(), StandardCharsets.UTF_8),
	true);
	ui.getPage().executeJs(js);
	} catch (IOException e) {
	LoggerFactory.getLogger(MetricsCollectorElement.class)
	.warn("Could not load observability-kit client code", e);
	}
	}

I suggest to extract e.g. a injectClientResource(UI, key, resource) to avoid duplication.

[caalador]

Extracted to Util for reuse when needed.

[heruan]

Why casting these two counters to long, while DistributionSummary below is kept double?

[caalador]

DistributionSummary.count() actually returns long and not double where as counter and functionCounter return double so they are cast to long to normalize the value to integer for the panel.

[heruan]

Do we need to evict history at some point?

[caalador]

The buffers themselves are set to 20 items, but a key is not removed at any point after it has been added. The list is thus persisted for the page lifetime.

Not certain if we need to clean it with the current key amount, but could be something to think about.