[openapi-to-tsp] Emit authentication defintion

[catalinaperalta]

For swagger definitions like this one:

"securityDefinitions": {
    "azure_auth": {
      "flow": "implicit",
      "authorizationUrl": "https://login.microsoftonline.com/common/oauth2/authorize",
      "scopes": {
        "user_impersonation": "impersonate your user account"
      },
      "type": "oauth2",
      "description": "Azure Active Directory OAuth2 Flow."
    }
  },

Could we support emitting the corresponding TypeSpec definition with @useAuth?