Key Vault: disable_public_network_access

[BlakeWills]

This PR closes #

The changes in this PR are as follows:

• Adds support for disabling public network access against key vault.
• Adds missing key permissions.

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:

let vault =
    keyVault {
        name "my-vault"
        // ...

        // new:
        disable_public_network_access
    }