feat(snowflake)!: Add OBJECT_KEYS transpilation to DuckDB

[kyle-cheung]

Documentation:

• Snowflake https://docs.snowflake.com/en/sql-reference/functions/object_keys
• DuckDB https://duckdb.org/docs/stable/data/json/json_functions#json-scalar-functions

[geooo109]

We should maintain only one representation for this AST node - JSONKeys(Func) is sufficient.

When adding a new function in SQLGlot, we search across all dialects (using their official documentation and manual testing) to determine if the function is supported elsewhere. This allows us to come up with the most generic AST node that supports all variations.

For example:

• Snowflake: OBJECT_KEYS(object) - single argument
• DuckDB: json_keys(json [, path]) - accepts an optional path argument (can be a single value or list)

With the current addition we only support a single argument, this will fail in future uses.

So, let's make a search among the dialects and check all the vacations, and make the representation generic.