Add regex in JSON schema to check date properties in ISO 8601 UTC format

[thehenrytsai]

See date format requirements in #113.

The regex should be added for dateCreated and datePublished properties.

[rajakash-dev]

Can you please elaborate on how to use the regex , i have built and tested a regex exp but not sure how to use it in this use case.

[thehenrytsai]

You can see regex examples in https://github.com/TBD54566975/dwn-sdk-js/blob/ecd72c95e4ab31f68dbd74d36bc3502967d163da/json-schemas/definitions.json used for validations.

[rajakash-dev]

#150

[duncanmak]

We can close this now!

[thehenrytsai]

Yes we can!