Add initial kosmos-postgresql cookbook

This is to install PostgreSQL all in one place instead of for each
service that needs it (Mastodon, ejabberd, ...)

site-cookbooks/kosmos-postgresql/CHANGELOG.md

@@ -0,0 +1,11 @@
+# kosmos-postgresql CHANGELOG
+
+This file is used to list changes made in each version of the kosmos-postgresql cookbook.
+
+# 0.1.0
+
+Initial release.
+
+- change 0
+- change 1
+