Support Express Container Apps environments and apps in resource tree

[philliphoff]

Problem

Azure Container Apps now supports Express environments (indicated by an environmentMode property set to Express on the managed environment resource). Express apps have their own portal at https://containerapps.azure.com, but the extension currently has no awareness of Express environments or apps.

Expected Behavior

• Express managed environments and their child container apps should be visually distinguished in the Azure resources tree (e.g. with an (Express) label).
• Express container apps should offer an "Open in Express Portal" context menu command that navigates to the Express portal.
• Expanding Express container app nodes should not error due to missing properties (e.g. scale) that may not be present on Express app templates.