Date validation improvements

[Maurier]

Revise our different schemas and make sure date validations are in place as follows:

• The publication date MUST be greater than or equal to the creation date.
• In the case where the publication date is a year, the year must be >= the year of the creation date.
• Do not compare the publication date to the modification date because it is possible in some instances that a resource could be modified after publication.

Additional technical limitations:

• $data reference syntax is not supported inside of anyOf schema definitions. This means that this type of validation is not possible for elements nested inside combinator schemas trying to access data outside.

https://ajv.js.org/guide/combining-schemas.html#data-reference

if the $data reference is inside a referenced subschema it cannot point to the data outside of the root level for this subschema)