Test case-sensitive table names in dbt-snowflake for `generate_source` macro

### Describe the feature

https://github.com/dbt-labs/dbt-codegen/pull/192 hardcoded an uppercase identifier for Snowflake due to the default quoting behavior for seeds in dbt-snowflake. Search `integration_tests/tests/test_generate_source_case_sensitive.sql` for `{% if target.type == "snowflake" %}` to see the specific section of code.

This means that the case-sensitive behavior introduced in https://github.com/dbt-labs/dbt-codegen/pull/168 is not fully tested for table names in dbt-snowflake specifically.

We would like to address that if possible.

One idea is to do something similar as in `integration_tests/macros/operations/create_source_table.sql` to create case sensitive database, schema, table, and column names.

### Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

### Additional context
Is this feature database-specific? Which database(s) is/are relevant? Please include any other relevant context here.

### Who will this benefit?
What kind of use case will this feature be useful for? Please be specific and provide examples, this will help us prioritize properly.

### Are you interested in contributing this feature?