Add a `Gitlab::Workhorse::ARCHIVE_FORMATS` constant and use that instead of separate definitions

We have several places where we show different formats to download an archive, we should consolidate that to 1 constant, perhaps in Gitlab::Workhorse since that's where the format is mapped to a Gitaly::GetArchiveRequest::Format.

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The following discussion from !19065 (merged) should be addressed:

• @reprazent started a discussion:

  I'm seeing these formats defined in quite a few places.

  I think we should move this into a constant, perhaps in Gitlab::Workhorse.

  I think we can do that in a separate issue though as we should also update these occurrences:

  File: app/models/releases/source.rb
  9:18:    FORMATS = %w(zip tar.gz tar.bz2 tar).freeze
  
  File: app/views/projects/buttons/_download_links.html.haml
  1:16:- formats = [['zip', 'btn-primary'], ['tar.gz'], ['tar.bz2'], ['tar']]
  
  File: spec/support/shared_examples/features/archive_download_buttons_shared_examples.rb
  4:22:  let(:formats) { %w(zip tar.gz tar.bz2 tar) }