PDJB-306: Add marked joint landlord flag

[samyou-softwire]

Ticket number

PDJB-306 (and others in the future)

Goal of change

adds a database column that tracks whether the user indicated this is a JL property

right now filled in from the outcome of this question on the registration journey

this will be used later on for designs where the landlord needs to specifically state later on that the property has no joint landlords

Description of main change(s)

adds database column

adds hooks into the journey flow to populate it

For reviewer

nothing here except the population of the field is feature flagged. I think this is fine as the default 'false' will be true for any registrations made before we turn on JL

Checklist

Delete any that are not applicable, and add explanation below for any that are applicable but haven't been done

• Screenshots of any UI changes have been added
• Unit tests for new logic (e.g. new service methods) have been added
• Test suite has been run in full locally and is passing
• Branch has been rebased onto main and run locally, with everything working as expected (both for your new feature
  and any related functionality)
• TODO comments referencing this JIRA ticket have been searched for and removed - if a future PR will address them,
  mention that here
• QA instructions have been added to the ticket (particularly if this is the last PR required to complete the ticket) (nothing to QA yet, this is an internal change)

[TomHanmer29]

Looks sensible to me! I think false by default is a good state for this to be in