Let no-unsupported-configs rule check in next.config.ts#896

Let the eslint rule that checks the next config file also check for the typescript variants, [which is now stable in next 15.](https://nextjs.org/docs/app/building-your-application/configuring/typescript#type-checking-nextconfigts) One could argue that only `js|mjs|ts` are needed since `mts|cts|cjs` are currently [not supported yet](https://github.com/vercel/next.js/pull/70376). But it shouldn't hurt to allow them in the regex for when/if they are supported.