Use lower case extension for setting datatype in data discovery

[bernt-matthias]

I thought that I already did this here, but apparently it was something else. So, now for real .. with a test.

When trying to find out what my original change does I found that DatasetMatcherFactory.matches_format and DatasetMatcherFactory.matches_any_format are unused. Should such code be removed?

How to test the changes?

(Select all options that apply)

• 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

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

[github-actions]

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

[mvdbeek]

Thanks @bernt-matthias. If you want to refactor things and remove dead code (yep, sure looks unused) I think it's always better to do that in a separate PR.