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>

site-cookbooks/kosmos-ejabberd/recipes/firewall.rb

@@ -25,13 +25,13 @@ firewall_rule 'erlang_cluster' do
 end
 
 firewall_rule 'ejabberd_stun_turn' do
-  port     node["kosmos-ejabberd"]["stun_turn_port"]
+  port     node["ejabberd"]["stun_turn_port"]
   protocol :udp
   command  :allow
 end
 
 firewall_rule 'ejabberd_turn' do
-  port     node["kosmos-ejabberd"]["turn_min_port"]..node["kosmos-ejabberd"]["turn_max_port"]
+  port     node["ejabberd"]["turn_min_port"]..node["ejabberd"]["turn_max_port"]
   protocol :udp
   command  :allow
 end