Migrate ejabberd uploads to mod_s3_upload and Garage

In addition to installing and configuring the new module, this also
enables public access to the S3 API via `bucket-name.s3.kosmos.org` as
well as Web access on `bucket-name.web.s3.kosmos.org` (when enabled).

Also includes some drive-by improvements to Chef attribute naming and
usage.

Co-authored-by: Greg Karékinian <greg@karekinian.com>

roles/ejabberd.rb

@@ -7,6 +7,7 @@ default_run_list = %w(
 
 production_run_list = %w(
   role[postgresql_client]
+  role[garage_gateway]
   kosmos-ejabberd::letsencrypt
   kosmos-ejabberd::default
 )

roles/openresty_proxy.rb

@@ -23,6 +23,7 @@ production_run_list = %w(
   kosmos_drone::nginx
   kosmos-ejabberd::nginx
   kosmos_garage::nginx_web
+  kosmos_garage::nginx_s3
   kosmos_gitea::nginx
   kosmos_gitea::nginx_ssh
   kosmos_rsk::nginx_testnet