Server: Naming convention should not change casing of custom enum values

### Version Information

Server Version: 2.10.1

### Environment

Cloud/ OSS

### What is the current behaviour?

Currently setting naming convention of `graphql-default` will enforce casing of enums, including custom enums.

### What is the expected behaviour?

Naming convention should only affect built-in enums, not custom user enums.

### How to reproduce the issue?

1. Create and track an enum table `CREATE TABLE (name TEXT PRIMARY KEY);`
2. Insert a value into this table, make sure it is lowercased.
3. Set this table as an enum.
4. Set `HASURA_GRAPHQL_EXPERIMENTAL_FEATURES=naming_convention`
5. Set the naming convention `graphql-default`
6. The enum variant is uppercased.

### Any possible solutions?

Avoiding the graphql-default naming convention

### Related issues

This was likely introduced in #8640

Start by reproducing the enum behavior described in this issue with the graphql-default naming convention, then compare the change introduced in #8640. Done means custom user enum values retain their stored casing while the naming convention continues to affect built-in enums.

Written by the indexing model from the issue text.