[Access] Add options to fail or warn when payer is not able to pay

[peterargue]

Problem Description

The transaction payer balance validation currently is either on or off. To support a more gradual rollout, it would be helpful to have an intermidiate step that recorded some metrics/logging when a payer's balance was low without failing validation.

Proposed Solution

Add a new CLI flag for payer balance validation that specifies whether or not to enforce the check:
--check-payer-balance-mode

• warn -> record a metric and log a debug message with details, but allow the tx
• enforce -> the same as warn, but do not allow the tx