added multiwarehouse handling

[jesshitchcock]

I want to get the Saas demo compatible with different warehouses. To do this we need to apply different SQL logic depending on the warehouse type. In this PR I added logic to include Snowflake SQL in the date functions and added a new cross db date diff function.

To test this you can add a new profile to your .dbt/profiles.yml that points at a snowflake warehouse:

lightdash_demo_saas_snowflake:
  outputs:
    dev:
      type: snowflake
      account: 
      user:
      private_key: 
      role: 
      database: 
      warehouse: SNOWFLAKE_DATABASE_STAGING
      schema: dbt_demo
  target: dev

Fill in snowflake credentials from 1password.
Then run the following to:

• temporarily update the dbt project name to lightdash_demo_saas_snowflake in dbt_profiles.yml
• seed data: dbt seed
• build models: dbt build -s models/demo/*
• set lightdash project to SaaS demo: lightdash config set-project and select SaaS demo
• create a preview: lightdash preview
• check if you can query from tables in the preview project.

[oli-rmsy]

Something in the back of my mind reminded me of this: https://docs.getdbt.com/reference/dbt-jinja-functions/cross-database-macros#date-and-time-functions

I think we can remove some logic here - and support all warehouses, by implementing the above dbt integrated macros.