feat: add drop_keys parameter to map operation

[shreyashankar]

Changes

• Implemented drop_keys feature in both MapOperation and ParallelMapOperation classes
• Updated syntax_check() methods to validate drop_keys configuration
• Modified execute() methods to apply drop_keys to the output

Details

• drop_keys allows users to specify a list of keys to be removed from the output
• Added appropriate error handling and type checking for drop_keys configuration

Testing

The new tests cover the drop_keys functionality in both scenarios:

1. When used in conjunction with LLM-based processing
2. When used as a standalone key-dropping operation