Show Deploy Boards for Environments in Folders

What does this MR do?

People may want to organize their environments by heavily relying on folders, but, while we fetched the deploy board data, we never properly parsed it or displayed it for users.

Here, we parse the deploy board data for children in setFolderContent, as that is where the children are assigned to a folder when loaded.

We also need to update the check in setDeployBoard, as size does not seem to exist on children environments. Instead, isFolder is used (which captures the same information we need as a simple boolean).

For #299612 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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