EMSL: Provide Data in Ingest Directory and Organize ETL Scripts

[vchendrix]

Implement EMSL data ingest per standardized requirements:

• Create an ingest/emsl subfolder.
• Place all EMSL data files in this directory, formatted as JSON lists (enclosed in brackets) and named using the convention emsl_00001.json, emsl_00002.json, etc.
• Ensure each file is limited to ~25 MB and contains only complete records.
• All files must conform to the latest release schema.
• Document and implement a file splitting strategy if necessary.
• All ETL scripts for EMSL should be placed in contrib/emsl.
• Ensure independent file validation is possible.
• Document the EMSL ingest process, folder structure, file format, and splitting strategy.

[madettmann]

#15