[Improve] When starting, check whether the environment variable "SEATUNNEL_HOME" exists or not.

[FlechazoW]

Purpose of this pull request

When starting, check whether the environment variable "SEATUNNEL_HOME" exists or not.

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/seatunnel/tree/dev/docs

[FlechazoW]

This is test result.