Describe 'pills' (and re-ingestion comments) in ingestion management in the registry

[CecSve]

In the registry section of the System Components, the different ingestion steps ('pills') should be explained (example).

It would also be good to define some comments that can be used by Data Products and Informatics when forcing a reingestion. This could either be documented in the internal documentation, but it may also be relevant for the public tech docs (if standardized categories can be defined for some issues).