BUG: Fix purchase line item rehydration and a bug in purchase line item to claim link

[josh-torre]

Description

resolves Link to Ticket

• Fixes the bug on the claims process where the claims <-> purchase line item relationships were not being rehydrated when the claims process is continued\
• Fixes a bug on the backend where an error would occur if there were preexisting claim <-> purchase line item relationships. It will now filter out any purchase line items that have already been associated with the claim

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• New and existing unit tests pass locally with my changes

[ZainabImadulla]

LGTM