Include Metabolomics data

[alexgrent]

Metabolomics data should be included as a new dataset

• Include Metabolomics as a Dataset
• Include Metabolomics example dataset
• Test

[alexgrent]

• Included Metabolomics dataset within the Reactome Backend API
• Added example dataset from Metabolights

IMPORTANT
DO NOT MERGE IN PRODUCTION!!

• Before merging and roll out more metabolite data should be included first.