r/gitea: Configure SMTP mailer

Gitea needs SMTP configuration in order to send e-mail notifications
about e.g. pull requests.  The `gitea_smtp` variable can be defined to
enable this feature.

roles/gitea/templates/app.ini.j2

@@ -36,11 +36,23 @@ OFFLINE_MODE     = false
 PATH = /var/lib/gitea/data/lfs
 
 [mailer]
+{% if gitea_smtp|d %}
+ENABLED = true
+PROTOCOL = smtp
+SMTP_ADDR = {{ gitea_smtp.addr }}
+SMTP_PORT = {{ gitea_smtp.port }}
+FROM = {{ gitea_smtp.from }}
+{% else %}
 ENABLED = false
+{% endif %}
 
 [service]
 REGISTER_EMAIL_CONFIRM            = false
+{% if gitea_smtp|d %}
+ENABLE_NOTIFY_MAIL                = true
+{% else %}
 ENABLE_NOTIFY_MAIL                = false
+{% endif %}
 DISABLE_REGISTRATION              = true
 ENABLE_CAPTCHA                    = false
 REQUIRE_SIGNIN_VIEW               = false