Add suppress_warnings argument to various metrics

The functions for computing individual metrics raise warning in edge cases (for example, when standard deviation is zero). In some cases this can result in multiple warnings which all have the same underlying cause. For example, in case of DSM the user will see a warning for each subgroup.

For users who call the tool from command line or using the top-level API function `run_*`, we could display a single warning pointing out the issue and suppress subsequent warnings raised by each function through an optional `suppress_warnings` argument. The default value will be `False`.

This would require carefully working through different metrics to make sure we do not suppress any unrelated warnings.