OCM plugin should have more verbose error card when backend is unavailable

[Zaperex]

What do you want to improve?

The OCM frontend error card

What is the current behavior?

Currently when the OCM backend is unavailable, the OCM frontend outputs an error card with a very generic error message: SyntaxError: Unexpected end of JSON input This does not tell the user much about what the actual issue is, and unless the user is familiar with this error they would have no idea this is due to the backend not being accessible. Ex: in the backstage-showcase, the ocm backend might be turned off.

What will the new behavior be?

The error card should instead inform the user that the backend might not be accessible or something more specific to the actual cause of the error.