[PM-17830] Backend changes for admin initiated sponsorships (#5531)

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* WIP

* Add `Notes` column to `OrganizationSponsorships` table

* Add feature flag to `CreateAdminInitiatedSponsorshipHandler`

* Unit tests for `CreateSponsorshipHandler`

* More tests for `CreateSponsorshipHandler`

* Forgot to add `Notes` column to `OrganizationSponsorships` table in the migration script

* `CreateAdminInitiatedSponsorshipHandler` unit tests

* Fix `CreateSponsorshipCommandTests`

* Encrypt the notes field

* Wrong business logic checking for invalid permissions.

* Wrong business logic checking for invalid permissions.

* Remove design patterns

* duplicate definition in Constants.cs

* Allow rollback

* Fix stored procedures & type

* Fix stored procedures & type

* Properly encapsulating this PR behind its feature flag

* Removed comments

* Updated ValidateSponsorshipCommand to validate admin initiated requirements

---------

Co-authored-by: Conner Turnbull <133619638+cturnbull-bitwarden@users.noreply.github.com>
Co-authored-by: Conner Turnbull <cturnbull@bitwarden.com>

src/Core/Constants.cs

@@ -141,6 +141,7 @@ public static class FeatureFlagKeys
     /* Billing Team */
     public const string AC2101UpdateTrialInitiationEmail = "AC-2101-update-trial-initiation-email";
     public const string TrialPayment = "PM-8163-trial-payment";
+    public const string PM17772_AdminInitiatedSponsorships = "pm-17772-admin-initiated-sponsorships";
     public const string UsePricingService = "use-pricing-service";
     public const string P15179_AddExistingOrgsFromProviderPortal = "pm-15179-add-existing-orgs-from-provider-portal";
     public const string PM12276Breadcrumbing = "pm-12276-breadcrumbing-for-business-features";