Currently a delegator cannot bond more funds after they join. To remedy this we should add a

• bond_extra extrinsic that allows the delegator increase their bond with non-locked funds,
• and a bond_rewards extrinsic that allows a user to take their rewards and directly use them to increase their bonded funds. The bond_rewards extrinsic isn't strictly necessary since a delegator could claim_rewards and then call bond_extra.

Should wait until #10694 is merged to start working on this.