Support names instead of indices in metainfo definition references

as discussed before, I don't get the url to the section if I adopt the following syntax:

data: m_def: ../upload/raw/movpe_app-def_schema.archive.yaml#/definitions/section_definitions/Chemical

I need the sequential index of my section, according to the ordering in "sections":

data: m_def: ../upload/raw/movpe_app-def_schema.archive.yaml#/definitions/section_definitions/0