[FEATURE]: List Available SQL Functions

### Describe what you want

Sometimes there are functions we need to add to our postgres database (RPC calls, onupdate functions, etc) which we don't implement through drizzle. The ts code with drizzle then needs to be written with these functions in mind and requires thorough documentation on our side. If drizzle introspect could somehow list all of the non-default active functions/changes made, then it would be extremely convenient.