feat: added snowflake warehouse vars config

[christopher-turnbull]

resolves #1280
docs dbt-labs/docs.getdbt.com/#

Problem

Currently, users can only specify Snowflake warehouses through model-level config blocks or project-level configurations in dbt_project.yml. There's no way to override the warehouse at runtime without modifying these files, which makes it difficult to dynamically change warehouses for different scenarios.

Solution

This PR adds support for overriding the Snowflake warehouse using dbt vars, which works for both dbt run and dbt test commands. Users can now specify a warehouse at runtime like:

dbt run --vars '{snowflake_warehouse: LARGE_WAREHOUSE}'
dbt test --vars '{snowflake_warehouse: LARGE_WAREHOUSE}'

This provides more flexibility for users who need to:

• Dynamically change warehouses without modifying model or project files
• Use different warehouses for different environments or contexts
• Override warehouse settings in CI/CD pipelines

All tests have been added and are passing, including specific tests for both run and test commands.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

Checklist

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