server: report duplicate entries in metadata lists using ToTxt instead of Show

This change is because in https://github.com/hasura/graphql-engine-mono/pull/2477, errors come out as
```
multiple declarations exist for the following allowlist : [CollectionName {unCollectionName = NonEmptyText {unNonEmptyText = "collection_1"}}]'
```
which is awfully messy. This changes it to
```
multiple declarations exist for the following allowlist: collection_1
```

This should improve error messages across the board -- e.g. `RoleName` has a nice `ToTxt` instance, while we used to use a derived `Show` instances. However, there might just be instances where the `Show` instance was better, bit hard to be sure based on scanning the code since we don't have test coverage for these errors.

Broken out of the allowlist PR since it affects more than just the allowlist.

PR-URL: https://github.com/hasura/graphql-engine-mono/pull/3470
GitOrigin-RevId: 7a2c29f17d9f15d840cb2f89caefcdd3aae44d25

server/src-lib/Hasura/RQL/Types/Metadata.hs

@@ -62,7 +62,6 @@ module Hasura.RQL.Types.Metadata
     mkSourceMetadata,
     mkTableMeta,
     noMetadataModify,
-    parseListAsMap,
     parseNonSourcesMetadata,
     rsmComment,
     rsmDefinition,
@@ -138,21 +137,22 @@ import Hasura.SQL.Tag
 import Hasura.Session
 import Language.GraphQL.Draft.Syntax qualified as G
 
--- | Raise exception if parsed list has multiple declarations
+-- | Parse a list of objects into a map from a derived key,
+-- failing if the list has duplicates.
 parseListAsMap ::
-  (Hashable k, Eq k, Show k) =>
+  (Hashable k, Eq k, T.ToTxt k) =>
   Text ->
   (a -> k) ->
   Parser [a] ->
   Parser (InsOrdHashMap k a)
-parseListAsMap t mapFn listP = do
+parseListAsMap things mapFn listP = do
   list <- listP
   let duplicates = toList $ L.duplicates $ map mapFn list
   unless (null duplicates) $
     fail $
       T.unpack $
-        "multiple declarations exist for the following " <> t <> " : "
-          <> tshow duplicates
+        "multiple declarations exist for the following " <> things <> ": "
+          <> T.commaSeparated duplicates
   pure $ oMapFromL mapFn list
 
 -- | Versioning the @'Metadata' JSON structure to track backwards incompatible changes.