fix(experiments): Adjust fingerprint computation

[jurajmajerik]

Problem

I've made a mistake when setting up the compute_metric_fingerprint method. Right now, it includes the entire stats_config object in the computation, when all we really care about is the stats.method. Going forward this will be problematic - if we add any new fields to stats_config, this will invalidate existing fingerprints.

Changes

Instead of stats_config, only include stats_config.method in the fingerprint.

This will invalidate timeseries data in ~20 production experiments. I will manually run recalculations for them.

How did you test this code?

Updated tests

[greptile-apps]

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[rodrigoi]