docs: added config entry for ldap allow_sign_up option, #7972

docs/sources/installation/configuration.md

@@ -427,6 +427,11 @@ Set to `true` to enable LDAP integration (default: `false`)
 ### config_file
 Path to the LDAP specific configuration file (default: `/etc/grafana/ldap.toml`)
 
+### allow_sign_up
+
+Allow sign up should almost always be true (default) to allow new Grafana users to be created (if ldap authentication is ok). If set to
+false only pre-existing Grafana users will be able to login (if ldap authentication is ok).
+
 > For details on LDAP Configuration, go to the [LDAP Integration]({{< relref "ldap.md" >}}) page.
 
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