feat: Add ML operator support matrix, and ideally compares coverage with other major framework such as scikit-learn

[zhenzhongxu]

It'll be nice to have an operator support matrix similar to Ibis', with coverages compare to
scikit-learn

[deepyaman]

I think #32 is sufficient for now. Will close this if sounds good to you, too.

It'll be nice to have an operator support matrix similar to Ibis', with coverages compare to
scikit-learn

Specifically, Ibis measures coverage of each of it's own backends automatically (i.e. not coverage of operations supported by individual backends, such as whether something you can do in Postgres can be done in raw Ibis). Measuring coverage against scikit-learn will need to be maintained somewhat manually.

[jitingxu1]

#32
#102

done