Enable monitoring agent to transmit to log analytics workspace

[craddm]

✅ Checklist

• You have given your pull request a meaningful title (e.g. Enable foobar integration rather than 515 foobar).
• You are targeting the appropriate branch. If you're not certain which one this is, it should be develop.
• Your branch is up-to-date with the target branch (it probably was when you started, but it may have changed since then).

🚦 Depends on

⤴️ Summary

For Azure Monitoring Agent to be able to connect to a log analytics workspace, the VM it is on must have a Managed Identity.

This PR gives each VM a system-assigned managed identity, allowing the transmission of logs and metrics from the VM to the log analytics workspace.

An alternative would be to create a single managed identity to be shared across all VMs as a user-assigned managed identity rather than a system-assigned one.

🌂 Related issues

Closes #1931

🔬 Tests

Deployed a new SRE and observed that the logs are appropriately populated in the log analytics workspace.

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[jemrobinson]

This is the correct fix. The identity of each VM should be distinct and system-managed identities are easier to manage than user-managed ones.

[jemrobinson]

LGTM