Add main playbook and example configs (PPL-139)

group_vars/all.yml.example

+---
+db:
+  name: sentry
+  user: sentry
+  password: changeme
+
+virtualenv_dir: /opt/venv
+
+sentry_url: http://sentry.example.com # no trailing slash!
+sentry_key: '$Uper5ekr!t'
+
+email:
+  backend: django.core.mail.backends.smtp.EmailBackend
+  send_from: sentry@sentry.example.com
+  host: localhost
+  port: 25
+  user: ''
+  password: ''
+  tls: false

hosts.example

+[dbservers]
+sentry.example.com
+
+[appservers]
+sentry.example.com
+
+[webservers]
+sentry.example.com

site.yml

+---
+# This playbook deploys the whole application stack in this site.
+
+- name: Apply common configuration to all nodes
+  hosts: all
+
+  roles:
+    - common
+
+- name: Deploy and configure the databases
+  hosts: dbservers
+
+  roles:
+    - db
+
+- name: Deploy and configure the application servers
+  hosts: appservers
+
+  roles:
+    - app
+
+- name: Deploy and configure the webservers frontends
+  hosts: webservers
+
+  roles:
+    - web