Add support for detecting existing relations/updating model

[gliter]

Currently when we run dbt run twice in the same session we will get exceptions that table already exist

 Caused by: org.apache.flink.table.catalog.exceptions.TableAlreadyExistException: Table (or view) default_database.joined_data already exists in Catalog default_catalog.

This task requires that we first investigate how it should be handled properly by DBT and then implement what is possible.