[APM][Metrics] Allow text panels in the metric dashboards (elastic#224426)

Closes elastic#224425 

## Summary

This PR adds support for the text panel in the APM dashboards inside the
metrics tab

## Testing 

⚠️  UPDATE: The dashboard won't be part of the PR so ⬇️ won't work now

 - with connection to edge oblt cluster: 
- Open Applications > Service Inventory and click on the `cart` (or any
EDOT .NET service) service
   - Go to the metrics tab
   - The dashboard should be visible 
  

![image](https://github.com/user-attachments/assets/58082514-7e10-4758-adcf-069b4b9a2109)

Author: jennypavlova

x-pack/solutions/observability/plugins/apm/public/components/app/metrics/static_dashboard/helper.ts

@@ -60,9 +60,8 @@ export async function convertSavedDashboardToPanels(
   const panels = panelsRawObjects.reduce((acc, panel) => {
     const { gridData, embeddableConfig, panelIndex, title } = panel;
     const { attributes } = embeddableConfig;
-    const { state } = attributes;
-    const layers =
-      state.datasourceStates?.formBased?.layers ?? state.datasourceStates?.textBased?.layers ?? [];
+    const datasourceStates = attributes?.state?.datasourceStates ?? {};
+    const layers = datasourceStates.formBased?.layers ?? datasourceStates.textBased?.layers ?? [];
 
     acc[gridData.i] = {
       type: panel.type,
@@ -75,7 +74,7 @@ export async function convertSavedDashboardToPanels(
           ...attributes,
           references: [],
           state: {
-            ...state,
+            ...(attributes?.state ?? {}),
             adHocDataViews: getAdhocDataView(dataView),
             internalReferences: Object.keys(layers).map((layerId) => ({
               id: dataView.id,