[WIP] Terraform scripts for Azure

[coderplay]

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 work?

Borrowed the ideas from AWS and GKE modules, but bumped to newer versions of those terraform modules inculdin helm/null/external.

Code changes

• [ ] Has Go code change
• [ ] Has CI related scripts change

Tests

• [ ] Unit test
• [x] E2E test
• [x] Manual test
• [ ] No code

Side effects

• [ ] Breaking backward compatibility
• [ ] Other side effects:

Related changes

• [ ] Need to cherry-pick to the release branch
• [ ] Need to update the documentation

Release Notes

Add terraform scripts for provisioning azure AKS, tidb-operator as well as tidb clusters.

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[codecov-io]

Codecov Report

Merging #3832 (15799d0) into master (bdff17a) will increase coverage by 0.01%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3832      +/-   ##
==========================================
+ Coverage   62.39%   62.41%   +0.01%     
==========================================
  Files         169      169              
  Lines       17970    17963       -7     
==========================================
- Hits        11213    11212       -1     
+ Misses       5673     5671       -2     
+ Partials     1084     1080       -4     

Flag	Coverage Δ
unittest	62.41% <ø> (?)

[coderplay]

The external IP of tidb service load balancer was stuck on <pending>.

  Warning  SyncLoadBalancerFailed  5m18s (x7 over 10m)  service-controller  Error syncing load balancer: failed to ensure load balancer: Retriable: false, RetryAfter: 0s, HTTPStatusCode: 403, RawError: Retriable: false, RetryAfter: 0s, HTTPStatusCode: 403, RawError: {"error":{"code":"AuthorizationFailed","message":"The client 'xxxx' with object id 'xxxxx' does not have authorization to perform action 'Microsoft.Network/virtualNetworks/subnets/read' over scope '/subscriptions/xxxx/resourceGroups/tidb-k8s/providers/Microsoft.Network/virtualNetworks/tidb-vpc/subnets/aks-subnet' or the scope is invalid. If access was recently granted, please refresh your credentials."}}

related issues: https://github.com/Azure/AKS/issues/1392 https://github.com/Azure/AKS/issues/486 https://github.com/Azure/AKS/issues/441 https://github.com/Azure/AKS/issues/357 https://github.com/Azure/AKS/issues/422