costs: Return cache result instead panic

[jkroepke]

Hi, sometimes,

azure-resourcegraph-exporter just panic, because of a HTTP 429 error:

{"level":"panic","caller":"azure-resourcemanager-exporter/metrics_azurerm_costs.go:407","msg":"unexpected status code: 429","query":"resource_id_monthly","timeframe":"Custom","subscriptionID":"81ae40e4-a73e-49ed-ae42-ad441988dd01","stacktrace":"main.(*MetricsCollectorAzureRmCosts).collectCostManagementMetrics\n\t/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:407\nmain.(*MetricsCollectorAzureRmCosts).collectRunCostQuery.func1\n\t/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:231\ngithub.com/webdevops/go-common/azuresdk/armclient.(*SubscriptionsIterator).ForEach\n\t/go/pkg/mod/github.com/webdevops/[email protected]/azuresdk/armclient/iterator.subscriptions.go:65\nmain.(*MetricsCollectorAzureRmCosts).collectRunCostQuery\n\t/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:229\nmain.(*MetricsCollectorAzureRmCosts).Collect\n\t/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:189\ngithub.com/webdevops/go-common/prometheus/collector.(*Collector).collectRun.func1\n\t/go/pkg/mod/github.com/webdevops/[email protected]/prometheus/collector/collector.go:380"}
panic: unexpected status code: 429

goroutine 8595 [running]:
go.uber.org/zap/zapcore.CheckWriteAction.OnWrite(0x0?, 0x0?, {0x0?, 0x0?, 0xc00056e160?})
	/go/pkg/mod/go.uber.org/[email protected]/zapcore/entry.go:198 +0x65
go.uber.org/zap/zapcore.(*CheckedEntry).Write(0xc00172c340, {0x0, 0x0, 0x0})
	/go/pkg/mod/go.uber.org/[email protected]/zapcore/entry.go:264 +0x3ec
go.uber.org/zap.(*SugaredLogger).log(0xc0001200a0, 0x4, {0x0?, 0x23?}, {0xc0018a9820?, 0xc00012a028?, 0xc0001200a0?}, {0x0, 0x0, 0x0})
	/go/pkg/mod/go.uber.org/[email protected]/sugar.go:295 +0xee
go.uber.org/zap.(*SugaredLogger).Panic(...)
	/go/pkg/mod/go.uber.org/[email protected]/sugar.go:153
main.(*MetricsCollectorAzureRmCosts).collectCostManagementMetrics(0xc0003997c0, 0x19?, 0xc0003806a0, {0xc0003a3c00, 0x33}, {0x2357915, 0xa}, 0xc0018a9ed8, {0xc00005ecaa, 0x6}, ...)
	/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:407 +0xc99
main.(*MetricsCollectorAzureRmCosts).collectRunCostQuery.func1(0xc000476660, 0xc00306bb18?)
	/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:231 +0x1db
github.com/webdevops/go-common/azuresdk/armclient.(*SubscriptionsIterator).ForEach(0xc000120050?, 0xc00306bcf0?, 0xc0018a9d00)
	/go/pkg/mod/github.com/webdevops/[email protected]/azuresdk/armclient/iterator.subscriptions.go:65 +0x1e2
main.(*MetricsCollectorAzureRmCosts).collectRunCostQuery(0xc0003997c0, 0xc0018a9ed8, 0xc000077e08?)
	/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:229 +0x2ed
main.(*MetricsCollectorAzureRmCosts).Collect(0xc0003997c0, 0x26343e0?)
	/go/src/github.com/webdevops/azure-resourcemanager-exporter/metrics_azurerm_costs.go:189 +0xab
github.com/webdevops/go-common/prometheus/collector.(*Collector).collectRun.func1()
	/go/pkg/mod/github.com/webdevops/[email protected]/prometheus/collector/collector.go:380 +0x98
created by github.com/webdevops/go-common/prometheus/collector.(*Collector).collectRun
	/go/pkg/mod/github.com/webdevops/[email protected]/prometheus/collector/collector.go:351 +0x13b

instead return a panic, I would like to see the possibility to return a cached response instead a crash.