[MM-16798] Add a Guest Accounts feature flag (#13231)

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

api4/user.go

@@ -104,7 +104,7 @@ func createUser(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 
 		if token.Type == app.TOKEN_TYPE_GUEST_INVITATION {
-			if c.App.License() == nil {
+			if c.App.License() == nil || !*c.App.License().Features.GuestAccounts {
 				c.Err = model.NewAppError("CreateUserWithToken", "api.user.create_user.guest_accounts.license.app_error", nil, "", http.StatusBadRequest)
 				return
 			}
@@ -1387,7 +1387,7 @@ func login(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	if user.IsGuest() {
-		if c.App.License() == nil {
+		if c.App.License() == nil || !*c.App.License().Features.GuestAccounts {
 			c.Err = model.NewAppError("login", "api.user.login.guest_accounts.license.error", nil, "", http.StatusUnauthorized)
 			return
 		}
@@ -1971,7 +1971,7 @@ func promoteGuestToUser(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if c.App.License() == nil {
+	if c.App.License() == nil || !*c.App.License().Features.GuestAccounts {
 		c.Err = model.NewAppError("Api4.promoteGuestToUser", "api.team.promote_guest_to_user.license.error", nil, "", http.StatusNotImplemented)
 		return
 	}
@@ -2011,7 +2011,7 @@ func demoteUserToGuest(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if c.App.License() == nil {
+	if c.App.License() == nil || !*c.App.License().Features.GuestAccounts {
 		c.Err = model.NewAppError("Api4.demoteUserToGuest", "api.team.demote_user_to_guest.license.error", nil, "", http.StatusNotImplemented)
 		return
 	}