Add blurb to Concept Exercises

Each Concept will have to define a _blurb_, which is a short description of the exercise.

In an earlier PR, a placeholder blurb has been added to the .meta/config.json file of each Concept Exercise. The placeholder blurbs should be replaced with an actual blurb for each Concept Exercise. Blurbs must be limited to 350 chars and will be truncated in some views.

For forked exercises, it might be useful to check how other tracks have defined their blurb.

The blurb will be displayed on a track's exercises page and on exercise tooltips. For example:

See the [Concept Exercise spec](https://github.com/exercism/docs/blob/main/anatomy/tracks/concept-exercises.md#file-metaconfigjson) for more information.

## Tracking

https://github.com/exercism/v3-launch/issues/23