Min Zhou

[WIP] Terraform scripts for Azure

3

### What problem does this PR solve? This PR add terraform scripts for provisioning azure AKS, tidb-operator as well as tidb clusters. ### What is changed and how does it...

Alert name should be PD_cluster_down_tikv_nums rather than PD_cluster_down_store_nums

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File: [/master/alert-rules.md](https://docs.pingcap.com/tidb/dev/alert-rules) the source of truth: https://github.com/tikv/pd/blob/master/metrics/alertmanager/pd.rules.yml#L4.

Need detailed steps on this recovery

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File: [/release-1.0/en/troubleshoot.md](https://docs.pingcap.com/tidb-in-kubernetes/v1.0/troubleshoot) > If a StorageClass exists in the cluster but the available PV is insufficient, you need to add PV resources correspondingly. How? The PV is supposed to be...