[stats] Add ability to specify effect priors

[lukesonnet]

Summary

Adds ability to add informative priors to bayesian analysis.

Passes those priors down to the stats engine and renders them at the bottom of the results table.

Testing

WIP

Screenshots

Org settings

Results (flat prior, see results and text at bottom)

Results (weakish informative prior, see results and text at bottom)

Results (very strong prior, see results and text at bottom)

TODO:

• [ ] Add analysis settings toggle (with warning that you shouldn't really change this midflight)
• [ ] Add custom report settings
• [ ] Add ability to config via config.yml

[github-actions[bot]]

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