update node api docs to include fee parameter for transaction broadcasts

[distractedm1nd]

celestiaorg/celestia-node#1484 introduces the following changes to the gateway requests:

All transaction endpoints now have a "fee" key needed in the JSON request. An example value for this can be 2000. This includes the following endpoints:

• SubmitPayForData
• Transfer
• Delegate
• BeginRedelegate
• Undelegate
• CancelUnbondingDelegation

[jcstein]

thank you @distractedm1nd - I don't think we have anything for Delegate, BeginRedelegate, Undelegate, CancelUnbondingDelegation have anything in the docs cc @YazzyYaz. it looks like SubmitPayForData and Transfer have it though!