Managed Identity: Support for federated identity credentials.

[ninjarobot]

The changes in this PR are as follows:

• Managed Identity: Support for federated identity credentials.

I have read the contributing guidelines and have completed the following:

• [x] Tested my code end-to-end against a live Azure subscription.
• [x] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] Updated the release notes with a new entry for this PR.
• [x] Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

arm {
    add_resources [
        userAssignedIdentity {
            name "cicd-msi"
            add_federated_identity_credentials [
                federatedIdentityCredential {
                    name "gh-actions-cred"
                    audience EntraIdAudience
                    issuer "https://token.actions.githubusercontent.com"
                    subject "repo:compositionalit/farmer:pull_request"
                }
            ]
        }
    ]
}