Update Line of Credit Transaction Interest Rate

As part of ongoing improvements to servicing in our revolving system, we have added the ability to update the interest rate of a specific transaction on a line of credit.

This can be used to support variable interest rates or policy changes to draw-specific rates like cash advances. Note that such changes cannot be applied retroactively through this endpoint, and that rate changes for compliance with the Servicemembers Civil Relief Act (SCRA) and the Military Lending Act (MLA) are better handled by the respective dedicated endpoints for those purposes.