Fix error prometheus gauge metrics_azurerm_reservation.go

[PaulPowershell]

Fix error prometheus gauge, attempt 5, actual 6

[PaulPowershell]

Hi @mblaschke, I fix an error on prometheus gauge for reservation.go :
panic: inconsistent label cardinality: expected 5 label values but got 6 in prometheus.Labels{"kind":"Reservation", "reservationID":"XXXXX", "reservationOrderID":"XXXX", "scope":"providers/Microsoft.Billing/billingAccounts/XXXXXX", "skuName":"Standard_D8ds_v5", "usageDate":"2024-03-04 00:00:00 +0000 UTC"}
i just delete scope from prometheus.labels, build and test with my own docker hub and now it's OK

[mblaschke]

[sonarcloud]

Quality Gate passed

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[mblaschke]

scope label should be there, so i've added it to the label list which i totally forgot to do