Add element_identifier and ext to inputs config file export

[bernt-matthias]

element identifiers are crucial for collections and need to be exposed in the inputs configfile export. it's too hacky to parse the identifier from the staging path (plus: the staging path is sanitised).

I suggest to make the element_identifier a list, because it is for collections (there the first list elements are collection identifiers and the last the element identifier of the dataset), such that users (tool developers) do not need to check if it is a list or a string.

TODO:

• [x] docs in xsd

How to test the changes?

(Select all options that apply)

• [x] I've included appropriate automated tests.
• [ ] This is a refactoring of components with existing test coverage.
• [ ] Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

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[jmchilton]

This seems great!

[jdavcs]

Thank you, @bernt-matthias!

[github-actions[bot]]

This PR was merged without a "kind/" label, please correct.