Prevent empty LDAP search from deactivating all users (#9879) (#9890)

* Backport of #9879 (Add option to prevent LDAP from deactivating everything on empty search)

* go fmtted

Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>
Co-authored-by: zeripath <art27@cantab.net>

modules/auth/auth_form.go

@@ -30,6 +30,7 @@ type AuthenticationForm struct {
 	SearchPageSize                int
 	Filter                        string
 	AdminFilter                   string
+	AllowDeactivateAll            bool
 	IsActive                      bool
 	IsSyncEnabled                 bool
 	SMTPAuth                      string

modules/auth/ldap/ldap.go

@@ -47,6 +47,7 @@ type Source struct {
 	Filter                string // Query filter to validate entry
 	AdminFilter           string // Query filter to check if user is admin
 	Enabled               bool   // if this source is disabled
+	AllowDeactivateAll    bool   // Allow an empty search response to deactivate all users from this source
 }
 
 // SearchResult : user data