feat(scicat-metadata): multiple schemas support

[MatthMig]

Re-implementation of PR: #178 following SciCat community suggestions

Motivation

Following issue: #173

It is a first step for the objective to ingest files of a complex structure in a facility.
This has full backwards compatibility.

Description

Adds the possibility to import a schema in another schema, opening the possibility to factorize our configs.

Here is the file structure:

resources/
├── modules/
│   └── ill.imsc.json.example       # Reusable ILL common metadata
├── d17.imsc.json.example         # D17-specific schema importing ILL module
└── panther.imsc.json                  # Could import ILL module + add panther-specific fields

In case of conflict, the importer has the priority over the imported.

Usage example

Module Schema (modules/ill.imsc.json):

{
  "id": "ill-module-001",
  "name": "ILL Common Metadata Module",
  "variables": {
    "pid": {"source": "NXS", "path": "/entry0/user/proposal", "value_type": "string"},
    "owner": {"source": "NXS", "path": "/entry0/user/name", "value_type": "string"}
  },
  "schema": {
    "pid": {"field_type": "high_level", "machine_name": "pid", "value": "<pid>", "type": "string"}
  }
}

Importing Schema (d17.imsc.json):

{
  "id": "d17-schema",
  "name": "D17 Instrument Example Schema",
  "import": ["ill-module-001"],
  "instrument": "D17",
  "order": 1,
  "selector": "filename:starts_with:/data/d17",
  "variables": {
    "detector": {"source": "NXS", "path": "/entry0/instrument/det", "value_type": "string"}
  },
  "schema": {
    "instrument_properties": {"field_type": "scientific_metadata", "value": {"det": "<detector>"}}
  }
}

The resulting schema will have variables and schema from both the module and the importer.