Emit multiple api-versions in our metadata file for multiple services

[lirenhe]

As we support multiple services with different api versions in one SDK package, we need to update meta.json to support this.
Please refer to the discussion in Azure/typespec-azure#3749 for more details.

[weidongxu-microsoft]

metadata.json will have a dict of tsp namespace -> version, e.g.

{
  "apiVersions":
  {
    "compute": "2025-04-01",
    "disks": "2025-01-02"
  }
}