[MM-37557] Move error out of client4 response (#18101)

* Return an error seperately from Response

* Remove BuildErrorResponse

* Drop Response.Error from model/client4.go

* Migrate require.Nil checks

* Migrate require.NotNil checks

* More manual fixes

* Move error check out of CheckOKStatus and CheckCreatedStatus

* Move error check out of CheckForbiddenStatus

* Move error check out of CheckUnauthorizedStatus

* Move error check out of CheckNotFoundStatus

* Move error check out of CheckBadRequestStatus

* Move error check out of CheckNotImplementedStatus and CheckRequestEntityTooLargeStatus

* Move error check out of CheckInternalErrorStatus

* Move error check out of CheckServiceUnavailableStatus

* Remove error check from checkHTTPStatus

* Remove remaining references to Response.Error

* Check previously unchecked errors

* Manually fix compile and linter errors

* Return error in CreateWebSocket methods

* Return error instead of *AppError in DoApi methods

* Manually fix bad replacments

* Conistently return Response and error

* Use err instead of seperate bool return value to indicate success

* Reduce ussage of model.AppError in web/oauth_test.go

* Remove client4.Must

* Check error in buf.ReadFrom

* Fix failing tests

api4/saml_test.go

@@ -16,9 +16,10 @@ import (
 func TestGetSamlMetadata(t *testing.T) {
 	th := Setup(t)
 	defer th.TearDown()
-	Client := th.Client
+	client := th.Client
 
-	_, resp := Client.GetSamlMetadata()
+	_, resp, err := client.GetSamlMetadata()
+	require.Error(t, err)
 	CheckNotImplementedStatus(t, resp)
 
 	// Rest is tested by enterprise tests
@@ -64,10 +65,12 @@ func TestSamlResetId(t *testing.T) {
 	})
 	require.Nil(t, appErr)
 
-	_, resp := th.Client.ResetSamlAuthDataToEmail(false, false, nil)
+	_, resp, err := th.Client.ResetSamlAuthDataToEmail(false, false, nil)
+	require.Error(t, err)
 	CheckForbiddenStatus(t, resp)
 
-	numAffected, resp := th.SystemAdminClient.ResetSamlAuthDataToEmail(false, false, nil)
+	numAffected, resp, err := th.SystemAdminClient.ResetSamlAuthDataToEmail(false, false, nil)
+	require.NoError(t, err)
 	CheckOKStatus(t, resp)
 	require.Equal(t, int64(1), numAffected)
 }