Add GUI Annotation Examples to Documentation

Currently there are three pages with examples on how to use the annotations in schemas:

1. https://nomad-lab.eu/prod/v1/staging/gui/dev/plot
2. https://nomad-lab.eu/prod/v1/staging/gui/dev/editquantity
3. https://nomad-lab.eu/prod/v1/staging/gui/dev/datatable

These are very useful but are currently hidden under the dev path with no means of finding them. Ideally they would be given a more permanent path and linked in the corresponding sections of docs/schema/elns.md.