Databricks: support INSERT BY NAME

[finchxxia]

Summary

This PR adds support for Databricks INSERT ... BY NAME syntax.

• Adds a by_name field to the Insert AST node.
• Parses BY NAME for the Databricks and Generic dialects.
• Preserves BY NAME when formatting the AST back to SQL.
• Adds test coverage for INSERT INTO ... BY NAME with both SELECT and WITH queries.
• Updates existing Insert AST construction sites with the default by_name: false.

Examples

INSERT INTO target BY NAME
SELECT 1 AS a;

INSERT INTO TABLE target BY NAME
WITH source AS (
    SELECT 1 AS event_data_id
)
SELECT event_data_id FROM source;

Testing

cargo test --test sqlparser_databricks test_databricks_insert_by_name
Relevant PostgreSQL INSERT regression tests