Date and Datetime field types should mention RFC3339 format in field description

[jasonbahl]

What problem does this address?

Any ACF Field that is added to the GraphQL Schema should include in the field description that it will return data in the RFC3339 format.

Since dates are returned as String, this will help consumers know what to expect.

What is your proposed solution?

Update the graphql_description for fields of the Date and DateTime field type (and others if I'm missing any)

What alternatives have you considered?

leaving things as is 🤷🏻‍♂️

Additional Context

No response