Investigate drop-in replacement for GenQuery2-based genquery iterator

[korydraughn]

• main - code + readme
• main - tests
• 4-3-stable - code + readme
• 4-3-stable - tests

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Enhancement

See this file for the GenQuery iterator implementation.
https://github.com/irods/irods_rule_engine_plugin_python/blob/0f5df8f07da2362511c094da12867789bbe24ed2/genquery.py

The motivation behind this is to allow people to take advantage of the new parser without needing change their existing code (too much).

Things to keep in mind:

• Developers must implement their own form of pagination when using GenQuery2
• Some GenQuery1 columns may not exist or may have been renamed