Fix hashed storage for attachments bugs

Closes #40280

See merge request gitlab-org/gitlab-ce!15482

(cherry picked from commit 1da5df70)

d3c781f7 add upload saver spec
313bf9cd refactor spec
21357deb fix hashed storage and updated spec
d3b0fbb3 add uploads restorer spec
dce5909a fix typo
ef08a96e add changelog
319dec77 refactor specs
30943bd9 fix spec
be945c38 fix spec
0ed17fdc use dynamic_path_segment for path
22219e89 refactor spec