Samples do not generate compliant OData Error responses

The samples tend to use IActionResult return types, which put error messages in the value property, or don't provide an error message at all instead relying solely on an HTTP status code. This does not adhere to the OData Error specification. In particular:

• The error response MUST be a single JSON object. This object MUST have a single name/value pair named error. The value must be a JSON object.
• This object MUST contain name/value pairs with the names code and message, and it MAY contain name/value pairs with the names target, details and innererror.

As a result, consumers that do adhere to the spec are not able to show error messages.

Examples of non-compliant responses:

No payload (error object omitted):
https://github.com/OData/AspNetCoreOData/blob/38338c0c38e219798446d62cb72277bca2675bb7/sample/ODataDynamicModel/Controllers/HandleAllController.cs#L93

Error object omitted, message in value:
https://github.com/OData/AspNetCoreOData/blob/38338c0c38e219798446d62cb72277bca2675bb7/sample/ODataDynamicModel/Controllers/HandleAllController.cs#L108