Resolve "In DAG minimal syntax, allow specifying args or kwargs additionally, if unambiguous"

This MR addresses #155 (closed) and adapts the tests and DAG documentation accordingly.

This makes the following syntax possible:

transform:
  - my_operation: foo
    kwargs:
      foo: bar
  - my_other_operation: [foo, bar, baz]
    kwargs:
      more: foo
  - my_other_operation: {foo: bar, baz: spam}
    args: [more, foo]

(Specifying args or kwargs additionally was not possible before.)

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up or squash option set
  • Changelog entry added
  • Version number bumped
  • Reviewed & approved by @herdeanu and/or @jeremiastraub

Related issues

Closes #155 (closed)