CLI: Modify `init` command to produce the new consolidated `data-source` section instead of `cosmos` options

[Aniruddh25]

As per this rfc #935, we need to create a consolidated data-source section instead of a separate cosmos section:

See this comment:
#935 (comment)

{
  "$schema": "dab.draft-01.schema.json",
  "data-source": {
    "database-type": "",
    "options": {
      "..."
    },
    "connection-string": "AccountEndpoint=https://localhost:8081/;AccountKey=REPLACEME;"
  }
}

[Aniruddh25]

@ayush3797 could you please pick this up? This has higher priority than rest of the issues you have for this milestone, and should have clear requirements.