Allow the lender to be an option as a borrower in the dropdown menu

[IsaacCheng9]

Specification

• The user may find it more intuitive to add themselves as a borrower if they want to split an expense evenly (including themselves).
• Currently, the workflow for this is:
  1. The lender subtracts their split from the total amount they paid (which may not be a straightforward calculation).
  2. This amount is the expense that they input into the app.
  3. They add the other people who are part of the split.
• With this change, the workflow would be:
  1. The lender adds the total amount they paid as the expense in the app (no subtraction required).
  2. They add themselves and the other people who are part of the split.