Enable Shared mode when installed as an aks addon by default

[justinmchase]

Is your feature request related to a problem? Please describe.

We are not using helm and don't want to introduce helm to our pipeline but we do need AGIC and the shared mode to be enabled. Please introduce a way to enable this without requiring a helm dependency.

Please either add a parameter to enable shared mode when installed via aks addon or just make it enabled by default or always enabled.

Describe the solution you'd like

Honestly, it should just be always on and not an option but I'd be ok with a cli flag or terraform flag that would allow us to enable it when installing agic.