FR: Support showing description in a UI tooltip rather than inline in value.schema (see #932)

[Gaspi]

See #932 for context. This is suggestion 2.

The title and description fields from the values schema files are meant for documentation and not user interface definition. As such, they are often defined in a more verbose or redundant way than is preferable in our context.

Move the longer description into a tooltip (a small icon that would display the text either on click or hover in a mini-popup) rather than a smaller font subtitle. Short description could be kept inline, as they are now. The display mode could also be controlled in values.schema.json:

  "x-onyxia": {
    "descriptionStyle": "tooltip/inline"
  }