Fix amazon_s3.yml config for FILE_UPLOAD_STORAGE=filesystem

[mayorova]

What this PR does / why we need it:

This PR fixes a confusing behavior when FILE_UPLOAD_STORAGE is set to filesystem explicitly.
It's not "broken" in the product, because it's assumed that when this env var is empty, filesystem is used, and when it's s3, then S3 is used for storage.

But when FILE_UPLOAD_STORAGE=filesystem is set explicitly, the application isn't loaded, with the error:

/home/dmayorov/.asdf/installs/ruby/3.1.5/lib/ruby/3.1.0/psych/visitors/to_ruby.rb:326:in `block in visit_Psych_Nodes_Alias': Unknown alias: filesystem (Psych::BadAlias)

because the amazon_s3.yml doesn't have a :filesystem alias.

There are some references that hint that filesystem is a potential valid value for FILE_UPLOAD_STORAGE:

• porta/openshift/system/.env

  Line 85 in c0ec886

  # FILE_UPLOAD_STORAGE=filesystem

• porta/config/examples/paperclip.yml

  Line 16 in c0ec886

  <<: *<%= ENV['FILE_UPLOAD_STORAGE'].presence || 'filesystem' %>

so I made some changes in the example config to prevent this config from failing.

Which issue(s) this PR fixes

-none-

Verification steps

Run the app with FILE_UPLOAD_STORAGE=filesystem and make sure no errors are thrown and the storage is set correctly.

Special notes for your reviewer:

[akostadinov]

Good catch, nice!