Add bronze-to-silver Snowflake template

[Sakeeb91]

Summary

• add a bronze-silver-snowflake template that ingests Frankfurter rates into Snowflake and promotes them to a curated silver snapshot
• document Snowflake setup, template usage, and configuration placeholders to align with existing template guidance
• include column-level and custom quality checks on both assets to meet the acceptance criteria for data validation

Testing

• not run (template only)

Closes #1221

[Sakeeb91]

Please supply real Snowflake credentials in .bruin.yml and run bruin validate when you’re ready to exercise the pipeline.