[feature] Structured Justification in the IsDependency Node

[mdeicas]

Is your feature request related to a problem? Please describe.

IsDependency nodes contain a justification explaining why they were created, but they are string justifications that look like "Derived from SPDX CONTAINS relationship", which makes it difficult to filter the nodes by a certain justification and is not best practices in general.

Describe the solution you'd like
The justification field should be structured and the possible justifications defined, such as with a GraphQL enum.

Describe alternatives you've considered
Leaving the field as is.

Additional context
Related issue on problems with IsDependency #966