Add schema validation and draft submissions support

Boris Doesborgrequested to merge
issue/webform_analysis-3487291:3487291-schema-validation-for into 8.x-1.x
  • Apply patch #3487291-4 for schema validation fixes
  • Add nullable: true to end_date field for proper validation
  • Add in_draft boolean field to support draft submission filtering
  • Improve webform analysis configuration schema completeness

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

Closes #3487291

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