Store metadata of project training

[juhoinkinen]

It could be valuable to store some info about training of a project, which could also be shown by the CLI commands and REST API /projects/{project_id} method.

Currently show-project outputs the following:

Project ID:        tfidf-fi
Project Name:      TF-IDF Finnish
Language:          fi
Vocabulary:        yso
Vocab language:    fi
Access:            public
Trained:           True
Modification time: 2023-04-21 10:33:16

Maybe some of the following data could be added:

• [x] training state: trained or not-trained
• [x] vocabulary state: loaded or not-loaded
• [x] timestamp of the training run
• [ ] version of Annif that has been used in training/learning the project
• [ ] number of documents used to train the project
• [ ] name(s) of the file(s) via which the documents was/were given when training the project
• [ ] used backend parameters
• [ ] backend name
• [ ] duration of the training run
• [ ] ~size of the model on disk~
• [ ] timestamp(s) of learning run(s)

Also some more details on the training data (what?) and something that now goes to the debug log (what?).

These data for could be stored e.g. in a metadata file data/projects/the_project/annif_metadata along with the model file(s).

Edit: converted bullet list to checkbox list.

[osma]

These are all good ideas. Also it could be useful to have a "failed" status for projects/backends where the initialization fails for some reason - but that means making the initialization more careful.

I think it makes sense to start small and implement status features one (or two) at a time in separate PRs. For example trained vs. not-trained would be a good start.

Marking the issue as Long term because there are so many ideas here, but that doesn't mean we could implement some of them very soon.

[osma]

Tagging with 0.48 to indicate that some work in this direction (but not everything) should be done in that release