Silence Performance Warnings

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ActivitySim runs often output many pandas PerformanceWarnings around pd.concat() that flood the terminal.

Until the root of the problem is addressed, this performance warning can be silenced by changing "default" to "ignore" in this line: https://github.com/ActivitySim/activitysim/blob/main/activitysim/core/config.py#L711

A setting should be added to either settings.yaml or logging.yaml to control whether performance warnings are reported.