[Bug][Seatunnel-web][Addendum] Escape seatunnel-web placeholders

[arshadmohammad]

Enum values were not converted to string properly, corrected it

Purpose of this pull request

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

[arshadmohammad]

Before Fix:

After Fix:

After fix default value is properly populated.