Make indices compatible with add_indent

Creates vector indicating rows to be indented from fmt_table1 or fmt_regression output that can be passed to kableExtra::add_indent.

indent_key(x, ...)

Arguments

x	fmt_table1, fmt_regression, or fmt_uni_regression object
...	further arguments passed to or from other methods.

Value

vector for use in kableExtra::add_indent() or otherwise