add metadata into text_chunks

[dayesouza]

Description

Add new metadata field to be added at the start of each chunk id, being considered as tokens in the max_tokens_per_chunk

Proposed Changes

• Removed unused columns (source_column, timestamp_column, timestamp_format, title_column, document_attribute_columns) from input_config.py and replaced them with a new metadata field.
• Updated load_file functions in csv.py and text.py to handle the new metadata field.
• Modified chunk_text.py and strategies.py to include metadata and line delimiters in chunking operations.
• Added a new configuration option GRAPHRAG_INPUT_DOCUMENT_METADATA to specify metadata columns in the env_vars.md and yaml.md documentation files.

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).