Deduplicate and update Importer list (table)

The Reference Documentation for VulnerableCode includes two copies of a table listing Importers with 3 fields:
- Importer Name
- Data Source
- Ecosystems Covered
The first copy is displayed under Importer Overview: https://vulnerablecode.readthedocs.io/en/latest/reference_importer_overview.html#importer-overview
The second copy is standalone: https://vulnerablecode.readthedocs.io/en/latest/importers_link.html#importers
The table currently lists 25 Importers but there are 37 importers listed under: https://github.com/nexB/vulnerablecode/tree/main/vulnerabilities/importers

The tasks are to:
- Update the list to match the code, likely with some indicator of the status of each importer - e.g., In development, Beta, Released or similar
- Sort the list in some coherent way - alpha order is probably easiest.
- Remove one copy - probably best to keep the separate section and change the title to List of Importers or similar

Stretch goal is to automate updates to the list.