Author-year Reference Style in `myst`

[HumphreyYang]

As discussed in QuantEcon/lecture-python-intro#495, cite:t seems to better fit the context in some situations (i.e., QuantEcon/lecture-python-intro#495 (comment)).

However, to maintain a uniform style, we need to further think about switching styles (in bulk) (quote @mmcky).

[mmcky]

@HumphreyYang we have addressed this using a global option setting in _config.yml. Can this be closed?