Add correspondence table(s)

Bonsai policy is to store data on its "native" scale, which means we need correspondence from one set to another. Traditionally, we would have 1 to 1 and 1 to N, but maybe it also makes sense to have approximate 1 to 1 matches, and to distinguish 1 to 1 that is official versus matches made by Bonsai team members.

@mfastudillo You know this as well as anyone, want to suggest something? We would need a table name and the names and data types of the columns, plus values to be added whenever we want to limit choices to a select few ([enumerated types](https://www.postgresql.org/docs/12/datatype-enum.html)).

Start by reading the issue discussion and the linked PostgreSQL enumerated-types documentation. Clarify whether correspondence includes 1-to-1, 1-to-N, approximate, and official mappings, then propose table names, column data types, and any constrained values. Done means the schema design and allowed values are agreed.

Written by the indexing model from the issue text.