feat: Update dependencies (sqlalchemy, singer-sdk) (#44)

# Description

- Update sqlalchemy, singer-sdk & snowflake-sqlalchemy to latest
avaiable versions
- Resolve Deprecation warning by replacing usage of
`SQLConnector.connection` with new child method
`SnowflakeConnector.execute`

closes: #28

#31 would be outdated if this gets merged, and I recommend we close
that.

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Co-authored-by: Edgar Ramírez-Mondragón <[email protected]>