[Feature][Connector-V2][OneSignal]Add OneSignal source conector

[TaoZex]

Purpose of this pull request

#3018
Add OneSignal source conector

Check list

• Code changed are covered with tests, or it does not need tests for reason:
• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/incubator-seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update change log that in connector document. For more details you can refer to connector-v2
  2. Update plugin-mapping.properties and add new connector information in it
  3. Update the pom file of seatunnel-dist

[hailin0]

LGTM

[EricJoy2048]

@TaoZex Please resolve conflicts.

[TaoZex]

@TaoZex Please resolve conflicts.

Thanks. I have resolved the conflict and passed the CI.