Dsi abstractions

[Vedant1]

• created one joint dsi_relations table in collection rather than one per ingested data source
• schema reader to load relations for data source into dsi_relations
• added sqlite reader to sqlite.py for a sqlite reader -> plugin writer workflow instead of just a plugin reader -> sqlite writer workflow
• updated er diagram writer to use data from collections not a sqlite db directly
• organized coreterminal to show sqlite reader use case and also er diagram writer

core.py

1. added sqlite reader capabilities in artifact_handler
2. close backends when unloading them
3. if table exists in current collection, new data is appended to it in transload()

[jpulidojr]

Combined sqlite class with new read, write. Made additional changes for upstream code CI tests