Allow modes `z` and `Z` for docker volumes

[bernt-matthias]

Fixes https://github.com/galaxyproject/galaxy/issues/18989

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

• [x] I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.