Add support for storage elements in RTS-GMLC parser.

Summary/Motivation:

We want to read storage data when importing RTS-GMLC data into Egret. This PR implements that capability.

Reads storage.csv when parsing RTS-GMLC format. To be used by Egret, the CSV file needs to have more fields than what is defined by the standard RTS-GMLC format. At the time this PR is being submitted, documentation for storage.csv is found at https://prescient--184.org.readthedocs.build/en/184/reference/file_formats/rts-gmlc/storage.html. That documentation will become part of the main Prescient documentation once this PR is merged into Egret main.

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