Support for Azure Secrets

[adamrtalbot]

New feature

I can't seem to find an existing issue for this. Support for secrets on Azure via Azure Key Vault.

Usage scenario

Use secrets when using the Azure executor.

Suggest implementation

In a similar manner to AWS or GCP. Possibly requires #3314.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.