gitea: Restrict SSH configuration

Since Gitea servers may be exposed directly to the Internet, it is
important to prevent SSH tunneling, lest the server become an ingress
point into the network.

Additionally, the *gitea* user should not be allowed to use password
authentication, as this would only work if the user actually has a
password (which it does not) and would result in shell access instead of
Gitea.

group_vars/gitea.yml

@@ -0,0 +1,8 @@
+sshd_agent_forwarding: false
+sshd_tcp_forwarding: false
+sshd_x11_forwarding: false
+sshd_config_matches:
+- object: User
+  pattern: gitea
+  password_auth: false
+  permit_tty: false