add a System.vendor_deleted_date property

[adamsachs]

Potential path for supporting the deletedDate GVL vendor property in our System model

Description Of Changes

Adds a vendor_deleted_date field to the System model which can store a backing vendor record's deletedDate from the GVL, or a comparable property from another vendor record source as needed.

Code Changes

• adds vendor_deleted_date field to the System model

Steps to Confirm

N/A

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation Updated
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

[adamsachs]

i will publish a 3.0.1 release on PyPI once this is merged

[adamsachs]

@pattisdr @NevilleS this is the (very minor) upstream fideslang update that's needed to enable this field being populated through our stack.

this one should be merged first as all the other PRs are dependent upon it 👍