[Provider] Server entities and models (#1370)

* Mock out provider models and service

* Implement CreateAsync, CompleteSetupAsync, UpdateAsync, InviteUserAsync and ResendInvitesAsync

* Implement AcceptUserAsync and ConfirmUsersAsync

* Implement SaveUserAsync and DeleteUserAsync

* Add email templates

* Add admin operations for providers

* Fix mail template names

* Rename roles

* Verify provider has provideradmin

* Add self hosted check to admin controller

* Resolve review comments

* Update sql queries

* Change create provider to use email instead of userId

src/Sql/dbo/Stored Procedures/ProviderUser_ReadByIds.sql

@@ -0,0 +1,18 @@
+CREATE PROCEDURE [dbo].[ProviderUser_ReadByIds]
+    @Ids AS [dbo].[GuidIdArray] READONLY
+AS
+BEGIN
+    SET NOCOUNT ON
+
+    IF (SELECT COUNT(1) FROM @Ids) < 1
+    BEGIN
+        RETURN(-1)
+    END
+
+    SELECT
+        *
+    FROM
+        [dbo].[ProviderUserView]
+    WHERE
+        [Id] IN (SELECT [Id] FROM @Ids)
+END