[Data catalog] Move proximity.dist_pin_to_pin CTAS query into the dbt DAG

[jeancochrane]

While we moved just about all of the CTAS queries into the DAG in #111, we left out proximity.dist_pin_to_pin because it requires a more complex solution. Create a separate PR to move proximity.dist_pin_to_pin into the DAG by defining a series of intermediate transformations that gradually expand the radius of the buffer.

See this comment thread for more context: #111 (comment)

Blocked by #111.