Infer PKs via uniqueness tests

[dlawin]

Is your feature request related to a problem? Please describe.
Having to tag every PK column with "primary-key" is an annoying amount of setup, especially when it's easy to infer the model's PKs from dbt tests without additional configuration for data-diff

Describe the solution you'd like
Infer the PK column(s) from uniqueness tests when no "primary-key" tag is present

We should consider including the primary key(s) in the output so that an incorrect assumption is more obvious