Add Azure Managed Identity authentication

[aidendipple]

Hi, great tool and I'd love to use it.

I've just built my IaC pipeline to stand up my database with no user/pwd and only Azure Active Directory authentication.

Is this something your tool can accommodate or add as an enhancement?

[nvarscar]

Seems like this should be possible based on DbUp/dbup-sqlserver#7

I, however, don't have access to Azure AD to test this so I might have to ask you to validate it once it's implemented.