Support loading the schema from `.ts` files

In GraphQL-Hive a [modular approach](https://github.com/kamilkisiela/graphql-hive/blob/main/codegen.mts#L5) is used to maintain the schema. We should load it which can be done with [`graphql-tools`](https://the-guild.dev/graphql/tools/docs/schema-loading) and a glob watcher to hot-reload it.