`current_schema()` not yet supported

[tbantle22]

This is used by the ORM we use in the Dolt workbench to initialize the database connection

getting_started-> SELECT * FROM current_schema();
server closed the connection unexpectedly
	This probably means the server terminated abnormally
	before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
psql (15.5 (Homebrew), server 15.0)

query: SELECT * FROM current_schema()

[Nest] 85570  - 04/12/2024, 3:24:48 PM   ERROR [ExceptionsHandler] Cannot read properties of undefined (reading 'current_schema')
TypeError: Cannot read properties of undefined (reading 'current_schema')
    at PostgresQueryRunner.getCurrentSchema (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/src/driver/postgres/PostgresQueryRunner.ts:408:24)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
    at PostgresDriver.connect (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/src/driver/postgres/PostgresDriver.ts:368:37)
    at DataSource.initialize (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/src/data-source/DataSource.ts:253:9)
    at ConnectionResolver.addConnection (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/src/connections/connection.resolver.ts:88:5)
    at DatabaseResolver.addDatabaseConnection (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/src/databases/database.resolver.ts:143:5)
    at target (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/node_modules/@nestjs/core/helpers/external-context-creator.js:74:28)
    at Object.addDatabaseConnection (/Users/taylor/go/src/github.com/dolthub/dolt-workbench/graphql-server/node_modules/@nestjs/core/helpers/external-proxy.js:9:24)