add netbox role for ensuring netbox is deployed as specified

The role takes over the deployment of netbox and its dependencies, while
still requiring the user to provide the netbox version, db password and
config as well as to set up a web server and handle stuff like creating
users, etc.

roles/netbox/meta/argument_specs.yaml

@@ -0,0 +1,12 @@
+argument_specs:
+  main:
+    options:
+      netbox__version:
+        type: str
+        required: true
+      netbox__db_password:
+        type: str
+        required: true
+      netbox__config:
+        type: str
+        required: true

roles/netbox/meta/main.yaml

@@ -0,0 +1,11 @@
+---
+dependencies:
+  - role: redis
+  - role: postgresql
+    vars:
+      postgresql__dbs:
+        - name: netbox
+          owner: netbox
+      postgresql__users:
+        - name: netbox
+          password: "{{ netbox__db_password }}"