fix(dpp): document factory wouldn't allow delete transitions for immutable document types

[pauldelucia]

Issue being fixed or feature implemented

DocumentFactoryV0 and SpecializedDocumentFactoryV0 were not allowing to create delete transitions if not document_type.documents_mutable(), but it should have been checking document_type.documents_can_be_deleted().

What was done?

Changed the check and wrote a test. Also renamed the error message about not being able to delete immutable documents.

How Has This Been Tested?

Wrote a test for deleting immutable but deletable document types.

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone