Auto top up API credits

Add an option to automatically top up API credits when the number of credits used reaches a low watermark. Both the low watermark and the top up amount should be configurable.

Nice to have would be a notification of a top up event. This can be any or all of a web hook, email and API dashboard.

An important use case is users of platforms integrating Venice AI requiring direct access to dedicated API credits, i.e., outside of the platform’s staked VVV based VCU allocation.

Without an automatic top up acquiring USD based credits either requires manual intervention by the platform operator or a sufficiently sized buffer of USD API credits to accommodate what could very well be unpredictable usage requirements. Both of these options are undesirable. An optional and configurable automatic top up would elegantly facilitate this use case.