fix: Remove trigger functions from schema cache and OpenAPI output

Trigger functions can't be called directly from SQL and can't be called
via the /rpc prefix either - it makes no sense to expose them in the
OpenAPI output. And we don't need to cache them in the schema cache
either.

Best practice would be to keep the trigger functions in a non-exposed
schema anyway.

CHANGELOG.md

@@ -17,6 +17,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #2107, Clarify error for failed schema cache load. - @steve-chavez
    + From `Database connection lost. Retrying the connection` to `Could not query the database for the schema cache. Retrying.`
  - #2120, Fix reading database configuration properly when `=` is present in value - @wolfgangwalther
+ - #1771, Fix silently ignoring filter on a non-existent embedded resource - @steve-chavez
+ - #2135, Remove trigger functions from schema cache and OpenAPI output, because they can't be called directly anyway. - @wolfgangwalther
 
 ## [9.0.0] - 2021-11-25