There is the concept of needing to have the frontend tell when a Filing is OPEN/CLOSED

Do the following to create this status:

• Add a new REOPEN UserActionType
• Add a new /reopen endpoint for a filing that will create the REOPEN user action on the filing object
  • Use the filing_validator.py to add checks for the endpoint to make sure the filing exists (valid_filing_exists) and add a new check to verify the filing is not already open (use latest user action to determine)
• Add a @model_validator(mode="after") to the FilingDTO to set a "state" field on the FilingDTO based on the following:
  • If the latest user action is SIGN, state should be CLOSED. Otherwise, state is OPEN
• Add pytests