Fixes the schema to allow `input.from`, `output.as` and `export.as` to be either a runtime expression string or object

Please specify parts of this PR update:

• [x] Specification
• [x] Schema
• [ ] Examples
• [ ] Extensions
• [ ] Use Cases
• [ ] Community
• [ ] CTK
• [ ] Other

Discussion or Issue link: #899

What this PR does: Fixes the schema to allow input.from, output.as and export.as to be either a runtime expression string or object

Additional information: Fixes the output of the dsl-reference.md, which still had wording from alpha1