Feature request - parameter for max gwei

[koen84]

ETH gas makes for a significant OpEx cost, which will increase when more subgraphs migrate to mainnet.

I'd like to propose, potentially configurable a max gwei cost. The allocation would only be renewed if the the agent detects current gwei (including the factor that the graph uses) to be lower than that. Potentially a timeframe like 24h before allocation expiration, the agent could start monitoring.