Fix(duckdb): Use CREATE OR REPLACE when registering secrets on cursor init to prevent an 'already exists' error

[erindru]

Prior to this PR, if you were using DuckDB secrets and more than 1 connection, you'd get the following error on subsequent connections:

Temporary secret with name 's3' already exists!

This PR creates secrets using CREATE OR REPLACE instead of just CREATE to prevent this.

Note that we don't use CREATE IF NOT EXISTS because we want updated credentials to replace existing credentials rather than continuing to use old credentials.