MM-10140: API Implementation for Schemes related Endpoints (#8615)

* Implement basic scheme CRUD endpoints.

* Get All Schemes (Paged) Endpoint and store plumbing.

* Add get teams/channels for schemes.

* Fix unit tests.

* Review fixes.

* More review fixes.

store/store.go

@@ -485,5 +485,6 @@ type RoleStore interface {
 type SchemeStore interface {
 	Save(scheme *model.Scheme) StoreChannel
 	Get(schemeId string) StoreChannel
+	GetAllPage(scope string, offset int, limit int) StoreChannel
 	Delete(schemeId string) StoreChannel
 }