Making column names lowercase to make output table schema compatible with the Lakehouse

[pankajskku]

Why are these changes needed?

The column names must be in lowercase in Lakehouse. Otherwise, it throws the following error:

(RayTransformFileProcessor pid=11614) --- Logging error ---

(RayTransformFileProcessor pid=11614) Traceback (most recent call last):

(RayTransformFileProcessor pid=11614)   File "/home/ray/anaconda3/lib/python3.10/site-packages/lakehouse/catalog.py", line 178, in create_table_from_pyarrow_and_input_table

(RayTransformFileProcessor pid=11614)     self.create_table(table_name, location, new_schema, new_partition_spec)

(RayTransformFileProcessor pid=11614)   File "/home/ray/anaconda3/lib/python3.10/site-packages/lakehouse/catalog.py", line 243, in create_table

(RayTransformFileProcessor pid=11614)     raise ValueError(f"Invalid column names. Column names must be lowercase and can contains numbers or underscore ('_').")

(RayTransformFileProcessor pid=11614) ValueError: Invalid column names. Column names must be lowercase and can contains numbers or underscore ('_').

Related issue number (if any).

[pankajskku]

@touma-I Can you please have a look and merge this?
Please let me know the tag to refer to this release in the DPK-inner?