Add a functionality to download the XSD schema files from the ISO website

[SebaLukas]

Describe your changes

Adding an ISO XSD schema downloader. With the additional argument the user automatically accepts the ISO license with downloading the XSD schemas

Issue ticket number and link

11

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [ ] I have made corresponding changes to the documentation
• [x] I read the contribution documentation and made sure that my changes meet its requirements

[barsnick]

@SebaLukas, please review my doc changes and, if okay, feel free to merge.