Change the AdminIdentityDbContext tablenames to be derived from appsettings

[bclementfidx]

My organization is looking to use your admin solutions over AdminUI, but a big pain point for us is that we leverage the AspNet* table names and ideally we'd like to be able to use your solution without having to maintain any ongoing code changes (i.e. TableConsts.cs)

Would you be willing to take a look at this PR? We really like your product and it's just as good (if not better) than AdminUI and we'd forever use it and help out with issues/features along the way...

[skoruba]

Thanks for your PR, let me test it, that is great idea. 👍