Azure input with basic collector for VM instances

[girodav]

What does this PR do

This PR adds a new input to collect Azure-related assets. To keep the PR at a reasonable size, only Azure VM instances assets collection is included.

Important notes

• The Subscription ID is used as cloud.account.id. While it might be more accurate to consider the 'Tenant' as the closest Azure equivalent to an 'account,' it's worth noting that the vast majority of resources we intend to gather information about are organized and grouped by subscription. This includes items like VM instances, storage, event hubs, and networks.
• The Azure instance ID, in its full length, is used as asset.id (see the generated sample below). While it may appear lengthy and somewhat redundant, it aligns with what is published in our Azure integrations.

Generated asset document sample

{
    "@timestamp": "2023-09-13T14:42:51.494Z",
    "asset.metadata.resource_group": "GIZASVM",
    "host": {
      "name": "host"
    },
    "cloud.region": "westeurope",
    "cloud.provider": "azure",
    "agent": {
      "ephemeral_id": "a80c69df-22dd-4f97-bfd2-14572af2b9d4",
      "id": "9a7ef1a9-0cce-4857-90f9-699bc14d8df3",
      "name": "worklaptop.fritz.box",
      "type": "assetbeat",
      "version": "8.9.0"
    },
    "input": {
      "type": "assets_azure"
    },
    "cloud.account.id": "12cabcb4-86e8-404f-a3d2-111111111111",
    "asset.kind": "host",
    "asset.id": "/subscriptions/12cabcb4-86e8-404f-a3d2-111111111111/resourceGroups/GIZASVM/providers/Microsoft.Compute/virtualMachines/gizasvmWindowsenterprise",
    "asset.ean": "host:/subscriptions/12cabcb4-86e8-404f-a3d2-111111111111/resourceGroups/GIZASVM/providers/Microsoft.Compute/virtualMachines/gizasvmWindowsenterprise",
    "asset.metadata.state": "VM running",
    "asset.type": "azure.vm.instance",
    "ecs": {
      "version": "8.0.0"
    }
  }

Additional remarks

The current stable version of the Azure SDK for Go doesn't have support for fakes/mocks. However, the good news is that they're actively addressing this issue. According to the information in this GitHub issue, support for fakes is expected to be included in the upcoming GA version scheduled for release in September. Given this, I've made the decision not to spend time on a temporary workaround for unit tests. Instead, I'll be utilizing the latest beta version of the SDK, which already incorporates the new fakes.

[elasticmachine]

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cc @girodav