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>

environments/production.json

@@ -16,14 +16,19 @@
     "droneci": {
       "public_url": "https://drone.kosmos.org"
     },
+    "ejabberd": {
+      "turn_ip_address": "148.251.83.201"
+    },
     "garage": {
       "replication_mode": "2",
       "s3_api_root_domain": "s3.kosmos.org",
       "s3_web_root_domain": "web.s3.kosmos.org",
       "s3_web_domains": [
+        "media.kosmos.chat",
         "s3.kosmos.social",
         "s3.community.kosmos.org"
-      ]
+      ],
+      "xmpp_upload_bucket": "kosmos-xmpp-uploads"
     },
     "gitea": {
       "domain": "gitea.kosmos.org",