[PLT-5639] Show a message when invited addresses are blocked (#6691)

* Show a message when invited addresses are blocked

When using the "Send Email Invite" functionality. Emails were sent to
domains that were not on the `RestrictCreationToDomains` list. This
would lead to users getting a message that they can't create an account
if they follow the link in the email.

This commit will check the email addresses before the mails are sent and
warn the user typing them in which ones are blocked.

* Add unit test for domain restrictions on invite

* Invite Member: Clear serverError on toggle

api4/team_test.go

@@ -1449,6 +1449,22 @@ func TestInviteUsersToTeam(t *testing.T) {
 			}
 		}
 	}
+
+	restrictCreationToDomains := utils.Cfg.TeamSettings.RestrictCreationToDomains
+	defer func() {
+		utils.Cfg.TeamSettings.RestrictCreationToDomains = restrictCreationToDomains
+	}()
+	utils.Cfg.TeamSettings.RestrictCreationToDomains = "@example.com"
+
+	err := app.InviteNewUsersToTeam(emailList, th.BasicTeam.Id, th.BasicUser.Id)
+
+	if err == nil {
+		t.Fatal("Adding users with non-restricted domains was allowed")
+	}
+	if err.Where != "InviteNewUsersToTeam" || err.Message != "api.team.invite_members.invalid_email.app_error" {
+		t.Log(err)
+		t.Fatal("Got wrong error message!")
+	}
 }
 
 func TestGetTeamInviteInfo(t *testing.T) {