Postgres information schema docs not surfaced

Postgres docs should surface things like https://www.postgresql.org/docs/9.1/static/information-schema.html when searching for `information schema` or `information_schema`. This is a critical part of the system and it's not discoverable through devdocs.

No files or tests are named. Start by tracing how DevDocs indexes and searches PostgreSQL documentation for the terms `information schema` and `information_schema`; done when the PostgreSQL information schema documentation is surfaced for those searches.

Vom Indexierungsmodell aus dem Issue-Text verfasst.