Fix Connection Config DPOs

[XJDKC]

Change the annotations from

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "authenticationTypeCode", visible = true)
@JsonSubTypes({
  @JsonSubTypes.Type(value = OAuthClientCredentialsParametersDpo.class, name = "1"),
  @JsonSubTypes.Type(value = BearerAuthenticationParametersDpo.class, name = "2"),
})

to

@JsonTypeInfo(
    use = JsonTypeInfo.Id.NAME,
    include = JsonTypeInfo.As.EXISTING_PROPERTY,
    property = "authenticationTypeCode")
@JsonSubTypes({
  @JsonSubTypes.Type(value = OAuthClientCredentialsParametersDpo.class, name = "1"),
  @JsonSubTypes.Type(value = BearerAuthenticationParametersDpo.class, name = "2"),
})

The reason for this change is that when visible = true and authenticationTypeCode is already a field in the class, the serialized json ends up including two authenticationTypeCode entries. For example:

{
  "connectionTypeCode": 1,
  "connectionTypeCode": "1",
  "uri": "https://myorg-my_account.snowflakecomputing.com/polaris/api/catalog",
  "remoteCatalogName": "my-catalog",
  "authenticationParameters": {
    "authenticationTypeCode": 1,
    "authenticationTypeCode": "1",
    "tokenUri": "https://myorg-my_account.snowflakecomputing.com/polaris/api/catalog/v1/oauth/tokens",
    "clientId": "client-id",
    "clientSecretReference": {
      "urn": "urn:polaris-secret:secretmanager-impl:keystore-id-12345",
      "referencePayload": {
        "hash": "a1b2c3",
        "encryption-key": "z0y9x8"
      }
    },
    "scopes": [
      "PRINCIPAL_ROLE:ALL"
    ]
  }
}

Setting include = JsonTypeInfo.As.EXISTING_PROPERTY ensures that it uses the existing field without duplicating it in the json.

Also some minor changes to the dpo classes:

1. Add NULL_TYPE to type enum
2. Remove authenticationTypeCode and connectionTypeCode from subtypes' constructor.

[dennishuo]

Nice find, thanks!