fix(APIM-608): make GovNotify properties optional (#1082)

## Introduction ✏️
Make `unsubscribe_link` and `scheduled_for` properties are set to
optional for strict schema validation.

## Resolution ✔️
* Set the `required` to false.

## Miscellaneous ➕
* Dependencies updates.
* Added additional validation scripts to `package.json`

---------

Co-authored-by: Abhi Markan <amarkan>