[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/openGraph_test.go

@@ -18,7 +18,7 @@ func TestGetOpenGraphMetadata(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()
 
-	Client := th.Client
+	client := th.Client
 
 	enableLinkPreviews := *th.App.Config().ServiceSettings.EnableLinkPreviews
 	allowedInternalConnections := *th.App.Config().ServiceSettings.AllowedUntrustedInternalConnections
@@ -59,8 +59,8 @@ func TestGetOpenGraphMetadata(t *testing.T) {
 		{"path": "/no-og-data/", "title": "", "cacheMissCount": 2},
 	} {
 
-		openGraph, resp := Client.OpenGraph(ts.URL + data["path"].(string))
-		CheckNoError(t, resp)
+		openGraph, _, err := client.OpenGraph(ts.URL + data["path"].(string))
+		require.NoError(t, err)
 
 		require.Equalf(t, openGraph["title"], data["title"].(string),
 			"OG data title mismatch for path \"%s\".")
@@ -70,6 +70,7 @@ func TestGetOpenGraphMetadata(t *testing.T) {
 	}
 
 	th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.EnableLinkPreviews = false })
-	_, resp := Client.OpenGraph(ts.URL + "/og-data/")
+	_, resp, err := client.OpenGraph(ts.URL + "/og-data/")
+	require.Error(t, err)
 	CheckNotImplementedStatus(t, resp)
 }