LB3 model import: convert definition of nested properties

[bajtos]

The syntax used for property definitions is slightly different between LB3 and LB4. The initial implementation of the import command is converting only top-level properties. We should convert nested properties too, both in anonymous objects and arrays.

An example of a model with nested properties:

{
  "name": "Product",
  "properties": {
    "rating": {
      "average": "number",
      "totalVotes": "number",
    }
  }
}

Acceptance criteria

• Implement the feature as described above, including automated tests
• Update Importing-LB3-models.md, remove the relevant point from the list of known limitations

[stale]

This issue has been marked stale because it has not seen activity within six months. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository. This issue will be closed within 30 days of being stale.

[stale]

This issue has been closed due to continued inactivity. Thank you for your understanding. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository.