Indexer visualisation for sources and sinks of datastreams

### Problem description
As a result of #5018 Guardian now supports sourcing data from arbitrary (user-defined) Hedera topics and outputting data into similarly defined Hedera topics. While data processed by Guardian policies is available for view in the Indexer it'd be helpful to have the pipeline graphically visualised.

### Requirements

1. Enhance Indexer back-end to track and index the relevant data from user-defined topics (for multi-workflow policies)
2. Adapt and extend existing visualisation in the Indexer to include sources and sinks of the data processed by Guardian policies so the entire evolution of the data set (such as product passport) can be visually represented.

### Definition of done

- Multi-workflow policy data, including sources and destinations, are depicted on the diagrams in the Indexer
- Guardian documentation updated

### Acceptance criteria
- Users can trace VC ancestry and evolution via the graphical user interface in the Indexer