Add support for Azure AD

[eloekset]

Same as PiranhaCMS#267 in the main repo

[eloekset]

One thing that is very tricky is that as long as Piranha.AspNetCore.Identity.SQLite is referenced by MvcWeb (or another Piranha application) it will override AzureAD authentication, and presents the Piranha login screen. I haven't figured out why that happens, but since I removed that dependency, the redirect to Azure AD for authentication works:

Since the App Registration in AD isn't complete yet, I don't get the necessary permissions, so I end up in a redirect loop. So configuring permissions and roles in Azure AD is the next step.

[eloekset]

Looks like all the fine grained permission claims needs a different treatment with Azure AD: https://stackoverflow.com/a/58907198/1421847

[eloekset]

Small update this evening. I've got rid of the redirect loop issue, but claims are still not configured correctly so the user doesn't get permission to use Manager after the token is retrieved. Result: