V3-repo-wide Report of completed exercises

It would be useful to have a report available of exercise names together with the language for all completed or substantially completed exercises in the V3 repo in concept/exercise name order.

In the event that we start to push parts of exercises to the repo rather than complete exercises then we should favour including anything with an _instrutions.md_ even if it is incomplete.

Nice to have would be to have links to the _instructions.md_ file. If the story name is available I suppose it would add some information but I don't think it is essential.

The purpose of the report is to allow a v3 track contributor to quickly inspect existing exercises to gain inspiration before starting work on a new exercise.

I don't know what the norm is for these sort of pages but if there are any constraints then a daily update would probably be sufficient.

The report can be used in conjunction with the curated [stories](https://github.com/exercism/v3/tree/master/reference/stories) document.

The issue names no files, tests, or entry points. Start by inspecting the repository structure and existing dashboard or report conventions, then determine how to enumerate V3 exercises in concept/exercise name order. Done means a report lists exercise names and languages for completed or substantially completed exercises, preferably linking instructions, with an acceptable update cadence.

Written by the indexing model from the issue text.