Support custom name for route server public IP

[Raaghavi]

This PR closes #

The changes in this PR are as follows:

• Route Server: Custom name support for Route Server Public IP.

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:

routeServer {
    name "my-route-server"
    public_ip_name "my-route-server-public-ip-name"
}

[ninjarobot]

Thanks for your contribution @Raaghavi - this is now in the 1.8.6 release and available on nuget.