Support loadbalancer ingress_address and private IPs

[Pedro Guimarães]

Following new Operator Framework and definition of schemas for relation data exchanged, we should add that feature to azure-integrator when it comes to lb-consumers.

One example is to standardize the choice of frontend IPs for the LB.

That is currently not possible using the charm.
One way to do so is by setting the ingress_address field on the request:
https://github.com/juju-solutions/loadbalancer-interface/blob/main/loadbalancer_interface/schemas/v1.py#L114

I believe that can be achieved by changing the following fields on the lib:
https://pastebin.ubuntu.com/p/xhrsdpPD84/

Where ingress_address field will be None if unset by the requiring side.
That will also expand the options available to allow selecting the frontend IP for both public and private VIPs.