Responsible for modifying the "flag" property of a specific milestone in the escrow to approve that milestone.
URL: /escrow/change-milestone-flag
contractId: ID (address) that identifies the escrow contract
milestoneIndex: Position that identifies the milestone within the group of milestones in the escrow
newFlag: New value for the "flag" property within the escrow milestone
client: Address of the client who will approve the milestone