Automatic merge from submit-queue (batch tested with PRs 47066, 48892, 48933, 48854, 48894)
azure: msi: add managed identity field, logic
**What this PR does / why we need it**: Enables managed service identity support for the Azure cloudprovider. "Managed Service Identity" allows us to ask the Azure Compute infra to provision an identity for the VM. Users can then retrieve the identity and assign it RBAC permissions to talk to Azure ARM APIs for the purpose of the cloudprovider needs.
Per the commit text:
```
The azure cloudprovider will now use the Managed Service Identity
to retrieve access tokens for the Azure ARM APIs, rather than
requiring hard-coded, user-specified credentials.
```
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: n/a
**Special notes for your reviewer**: none
**Release note**:
```release-note
azure: support retrieving access tokens via managed identity extension
```
cc: @brendandburns @jdumars @anhowe
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