stats: make --infer-boolean configurable

[jqnatividad]

Currently, booleans are inferred when --infer-boolean is enabled. The heuristic for inferring booleans is as follows:

• When a column's cardinality is 2, and;
• the 2 values' first characters are 0/1, t/f & y/n case-insensitive

Make it so the the first character heuristic is configurable, as t/f (True/False) and y/n (Yes/No) are English-centric.

Further, allow the user to specify more than just the first character, to eliminate false positives (e.g. A column whose cardinality is 2, and a domain of "Tom", "Frank" will be incorrectly inferred as boolean).