Subnet: Support `depends_on`

[ninjarobot]

This PR closes #

The changes in this PR are as follows:

• Subnets: Support for depends_on when defining standalone subnets.

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
        [
            subnet {
                name "subnet1"
                link_to_unmanaged_vnet (virtualNetworks.resourceId vnetName)
                prefix "10.28.0.0/24"
            }
            // `subnet2` will not be deployed until the `subnet1` resource is deployed.
            subnet {
                name "subnet2"
                link_to_unmanaged_vnet (virtualNetworks.resourceId vnetName)
                prefix "10.28.1.0/24"
                depends_on (subnets.resourceId (ResourceName vnetName / ResourceName "subnet1"))
            }
        ]
}

[ninjarobot]

@Huaxinli123 please review and let me know if this addresses your need for depends_on support in the subnet builder.

[ninjarobot]

Thanks for confirming the fix @Huaxinli123 - will merge and release this soon.