Change defaults for CHUNK_SIZE, CHUNK_OVERLAP and GLEANINGS

[AlonsoGuevara]

Description

Change default values for chunk size, chunk overlap and gleanings. This settings are based on various experimentations we did comparing a small chunk size and overlap against a big chunk size with multiple retries over the same one. This config yields an "almost the same" level of results while reducing cost and runtime.

Related Issues

#431 #385

Checklist

• [ ] I have tested these changes locally.
• [ ] I have reviewed the code changes.
• [ ] I have updated the documentation (if necessary).
• [ ] I have added appropriate unit tests (if applicable).