Update sqlpackage release notes with known issue

We found an issue for sqlpackage 18.5 where importing a bacpac with sensitivity classification using the .NET Core sqlpackage fails because of this known issue in Microsoft.Data.SqlClient. The fix is currently in the preview release of Microsoft.Data.SqlClient, so DacFx will be updated once the fix is in the stable release.

Author: kisantia

docs/tools/release-notes-sqlpackage.md

@@ -70,6 +70,7 @@ Thanks.  GeneMi (MightyPen in GitHub).  2019-03-27
 | Feature | Details |
 | :------ | :------ |
 | Deployment |  A regression was introduced in 18.5 causing there to be an “Incorrect syntax near 'type'” error when deploying a dacpac or importing a bacpac with a user with external login to on premise. Workaround is to use sqlpackage 18.4 and it will be fixed in the next sqlpackage release. | 
+| .NET Core | Importing bacpacs with Sensitivity Classification fails with "Internal connection fatal error" because of this [known issue](https://github.com/dotnet/SqlClient/issues/559) in Microsoft.Data.SqlClient. This will be fixed in the next sqlpackage release. |
 |   |   |
 
 ## 18.4.1 sqlpackage