Improve feedback on invalid dates

[duncandewhurst]

Badly formatted dates (e.g. 01/01/2021) and invalid dates (e.g. 0000-00-00T00:00:00Z) both result in the same feedback to users:

Incorrect date format. Dates should use the form YYYY-MM-DDT00:00:00Z. Learn more about dates in OCDS.

For dates that have the correct format but which are invalid, it would be helpful to prompt users to check for dummy values.

Example

{
   "publishedDate": "0000-00-00T00:00:00Z",
   "releases": [
      {
        "date": "01/01/2021"
      }
   ]
}