Inventory classification change - fix birthPeriod validation

[cookeac]

birthPeriod was previously specified as an icarDateType, which is half-right, because it is a date range.
Most validators interpret "format": "date" as an RFC3339 date, which does not allow for ranges.

Instead I have changed its type to string, and defined a pattern with a regex. If this is too complex we can ditch the regex and simply make it a string with the current description.

[erwinspeybroeck]

No comment from my side

[AndreasSchultzGEA]

• the 2 parts differ. whereas the first one is very flexible, the second one is fixed to YYYY-MM-DDZ
• the first part offers the possibility to insert YYYY-99, e.g. by defining [0-9]{2} as month
• Is the second part really optional? I think not. The separator as well.

[cookeac]

Having tested this in https://regex101.com/ there are three effective captures:

• ([0-9]{4}) - four digits (anything from 0000 to 9999 but effectively designed as year)
• ([0-9]{4}-[0-9]{2}) - four digits, a dash, and 2 digits. Intended to represent YYYY-MM but as you say it does allow for 9999-99. I will make a change to allow 00 to 19 for months (because more than that makes the regex complex).
• ([0-9]{4}-[0-9]{2}-[0-9]{1,2}(Z?)(\/|--)[0-9]{4}-[0-9]{2}-[0-9]{1,2}(Z?))) - intended to be YYYY-MM-DDZ/YYYY-MM-DDZ
  The Zs are optional (indicated by the question mark after them), but we could remove them completely. The only optionality then is whether you have a / or -- symbol. The latter is an alternative more suited to some operating systems.

So I think the optionality is right, but would be willing to accept corrections :-)
The remaining questions are:

• Do we even want the Z given that we just have dates and not times? I will remove if not.
• Do we want more sophisticated regex that enforces the exact day and month syntax? Otherwise I will just make changes that get us in the right approximate range - for instance 00-19 month and 00-39 days. This is easy.