[23.1] Fix discarded dataset ordering in Storage Dashboard

[davelopez]

Fixes #16898

When you delete an output of a tool the HDA size is null, by default, Postgresql seems to sort null values first. This change uses the correct null sorting for the size attribute in each case.

Before

After

How to test the changes?

• 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.

[martenson]

thanks @davelopez !