[23.1] Add HEAD route to job_files endpoint

[mvdbeek]

This is to make sure resuming downloads works out of the box (it should already work if nginx_x_accel_redirect_base or apache_xsendfile is set up).

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.

[jmchilton]

So cool - what a clean fix.