Add a template for new servers installation

.gitlab/issue_templates/new-server.md

+/title Install the new bare metal server(s) for <project> \
+/milestone %<milestone>
+
+Orders: <link to the mybox directory containing the order/delivery orders/...>
+Inventory: <link to the inventory page>
+
+Summary:
+- Management address (DNS): XXX.XXX.XXX.XXX (abcd.inria.fr)
+- VLAN configuration: VLANXXXX/VLANXXX
+- Internal IP(s): xxx.xxx.xxx.xxx
+- Internal DNS name(s): xxx.internal.(softwareheritage.org|<environment>.swh.network
+
+/todo Declare the servers in the [inventory](https://inventory.softwareheritage.org)
+/todo Add the management info in the credential store
+/todo Install the OS
+/todo Add puppet configuration (if needed)
+/todo Configure firewall rules (if needed)
+/todo <other actions if needed>