Fix dropping schema cache reload notifications

* test: bad schema reload
* refactor: DRY using the "extra" lib
* refactor: move worker funtions inside AppState
* Also rename Workers.hs to Admin.hs

postgrest.cabal

@@ -34,7 +34,8 @@ library
   default-extensions: OverloadedStrings
                       NoImplicitPrelude
   hs-source-dirs:     src
-  exposed-modules:    PostgREST.App
+  exposed-modules:    PostgREST.Admin
+                      PostgREST.App
                       PostgREST.AppState
                       PostgREST.Auth
                       PostgREST.CLI
@@ -70,7 +71,6 @@ library
                       PostgREST.Response.OpenAPI
                       PostgREST.Response.GucHeader
                       PostgREST.Version
-                      PostgREST.Workers
   other-modules:      Paths_postgrest
   build-depends:      base                      >= 4.9 && < 4.17
                     , HTTP                      >= 4000.3.7 && < 4000.5
@@ -86,6 +86,7 @@ library
                     , contravariant-extras      >= 0.3.3 && < 0.4
                     , cookie                    >= 0.4.2 && < 0.5
                     , either                    >= 4.4.1 && < 5.1
+                    , extra                     >= 1.7.0 && < 2.0
                     , fuzzyset                  >= 0.2.3
                     , gitrev                    >= 1.2 && < 1.4
                     , hasql                     >= 1.6.1.1 && < 1.7