Organize SKOS files

Currently, from the `GraphQL` spec, `skos` skeleton is initialized and outputs a file.

If this file is located in the same repo as the specification, it would mean:
```
Example_X/
├── spec/
│ ├── schema_1.graphql
│ ├── schema_2.graphl
│ └── schema_N.graphl
├── skos/
│ ├── skos.ttl
```
Here, `skos.ttl` will have concepts for objects and fields coming from the specified graphql schemas.

The output of it should be better structured as:

```
Example_X/
├── spec/
│ ├── schema_1.graphql
│ ├── schema_2.graphl
│ └── schema_N.graphl
├── skos/ *
│ ├── skeleton/ *
│ | ├──object_concepts.ttl *
│ | ├──field_concepts.ttl *
│ ├── extensions/
│ | ├──concept_scheme_A.ttl
│ | ├──concept_scheme_B.ttl
│ | ├──concept_scheme_ETC.ttl
│ | ├──... # Possible extensions to the concepts of the skeleton (e.g., synonyms, other languages, etc.)
```

`*` indicates those that should be created during the initialisation.

Start from the GraphQL specification flow that initializes the SKOS skeleton and currently writes skos.ttl; inspect how its output path and generated concepts are assembled. Done means initialization creates the requested skos/skeleton directory with separate object_concepts.ttl and field_concepts.ttl files, while leaving extensions available for additional concept schemes.

Written by the indexing model from the issue text.