SeaTunnel 2.1.3 released! Introducing in Assert Sink connector and NullRate, Nulltf Transform

More than a month after the release of Apache SeaTunnel(Incubating) 2.1.2, we have been collecting user and developer feedback to bring you version 2.1.3. The new version introduces the Assert Sink connector, which is an inurgent need in the community, and two Transforms, NullRate and Nulltf. Some usability problems in the previous version have also been fixed, improving stability and efficiency.