Thorough review of OSO docs to ensure they reference latest data model and API

[ccerv1]

I did a first pass last week to reflect the updated OSSD schema, but it's worth a thorough page-by-page review to make sure everything is up-to-date.

Most important is to check that anything that references the API is visible in the Hasura explorer and has the V1 postfix and all SQL queries still work in BigQuery.

[ccerv1]

@ryscheng per our discussion today, will remove pages like this one and instead add links to dbt-generated docs on models.opensource.observer. See also #959