Enable the errorAssertions govet check for mattermost-server code (#17346)

* Enable the errorAssertions govet check for mattermost-server code

* Removing unnecesary change

* Fixing some tests

* Fixing tests

* Fixing more after merge

* Fixing new offending entries

* Fixing small vet checks

* Fixing new cases detected by govet

* Fixing remote_cluster_test errors

* Fixing assertion

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

Makefile

@@ -603,7 +603,7 @@ vet: ## Run mattermost go vet specific checks
 		echo "mattermost-govet is not installed. Please install it executing \"GO111MODULE=off GOBIN=$(PWD)/bin go get -u github.com/mattermost/mattermost-govet\""; \
 		exit 1; \
 	fi;
-	@VET_CMD="-license -structuredLogging -inconsistentReceiverName -inconsistentReceiverName.ignore=session_serial_gen.go,team_member_serial_gen.go,user_serial_gen.go -emptyStrCmp -tFatal -configtelemetry"; \
+	@VET_CMD="-license -structuredLogging -inconsistentReceiverName -inconsistentReceiverName.ignore=session_serial_gen.go,team_member_serial_gen.go,user_serial_gen.go -emptyStrCmp -tFatal -configtelemetry -errorAssertions"; \
 	if ! [ -z "${MM_VET_OPENSPEC_PATH}" ] && [ -f "${MM_VET_OPENSPEC_PATH}" ]; then \
 		VET_CMD="$$VET_CMD -openApiSync -openApiSync.spec=$$MM_VET_OPENSPEC_PATH"; \
 	else \