Update soroban surge pricing test to using rolling average

[sydneynotthecity]

Background:

We want a way to be alerted if there are outlier events that impact Soroban inclusion fees. If the fee spikes suddenly, we want to be notified so that we can monitor network health. The current alert definition is too noisy and we ignore because it alerts any that Soroban enters pricing.

We care about two aspects of pricing:

1. if the inclusion fee spikes super high (higher than expected),
2. if the network sustains surge pricing for a longer duration than expected

We should

• Update the alert to use a rolling average of the inclusion_fee
• Perform analysis to determine historical outliers, which will help define a better heuristic for measuring outliers,
• Alert when the inclusion fee is N+ standard deviations outside a rolling average