[Improve][SeaTunnel-Web] Change JobMode and EngineType to enum type to avoid hard coding

[wuchunfu]

Purpose of this pull request

Change JobMode and EngineType to enum type to avoid hard coding

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

[wuchunfu]

@arshadmohammad @Hisoka-X PTAL, thanks