referencing a "definitions" file into another "definitions" file

To complete the cases showed in last comment of #954:

Keep in mind the discussion already made in #924 (closed)

We would like to support this

section: ../upload/raw/Substance.schema.archive.yaml#Substance 

as an alternative to this

section: Substance 

---

definitions:
  name: 'Electronic Lab Notebook schema fot MOVPE-STO'
  sections:
    Substance:
      base_section: nomad.datamodel.data.EntryData
      quantities:
        comment:
          type: str
          m_annotations:
            eln:
              component: StringEditQuantity
    MovpeSto_schema: 
      base_section: nomad.datamodel.data.EntryData
      m_annotations:
        eln:
          dict()
      sub_sections:
        materials:
          repeats: true
          section:
            m_annotations:
              eln:
                dict()
            sub_sections:
              substrate:
                repeats: true
                section: 
                  base_sections:
                    - nomad.datamodel.data.EntryData
                  m_annotations:
                    eln:
                      dict()
                  sub_sections:
                    composition:
                      repeats: true
                      section: Substance 

It would be nice to inherit from sections defined in separate files:

definitions:
  name: 'Electronic Lab Notebook schema fot MOVPE-STO'
  sections:
    Substance:
      base_section: nomad.datamodel.data.EntryData
      quantities:
        comment:
          type: str
          m_annotations:
            eln:
              component: StringEditQuantity
        chemical_name:
          type: str
          description: The name of the chemical that is typically used in literature
          m_annotations:
            eln:
              component: StringEditQuantity

    MovpeSto_schema: 
      base_section: nomad.datamodel.data.EntryData
      m_annotations:
        eln:
          dict()
      sub_sections:
        materials:
          repeats: true
          section:
            m_annotations:
              eln:
                dict()
            sub_sections:
              substrate:
                repeats: true
                section: 
                  base_sections:
                    - nomad.datamodel.data.EntryData
                  m_annotations:
                    eln:
                      dict()
                  sub_sections:
                    composition:
                      repeats: true
                      section: ../upload/raw/Substance.schema.archive.yaml#Substance