Fix publisher connections documentation (#269)

* Fix publisher connections documentation

- Fix connections format from object to array syntax
- Clarify that local parquet files don't need connection config
- Add DuckDB attached databases examples (BigQuery, Snowflake, PostgreSQL)
- Update all database connection examples with correct format

Signed-off-by: James Swirhun <james@ms2.co>

* docs: fix publisher config format in connections and publishing guides

- Use array format for connections with `name` field inside objects
- Add type-specific nested configs (postgresConnection, bigqueryConnection, etc.)
- Add DuckDB attached databases documentation
- Clarify --init flag usage and state persistence behavior

Signed-off-by: James Swirhun <jswir@users.noreply.github.com>
Signed-off-by: James Swirhun <james@ms2.co>

---------

Signed-off-by: James Swirhun <james@ms2.co>
Signed-off-by: James Swirhun <jswir@users.noreply.github.com>

Author: jswir