Identify whether sveltekit generate the project using typescript or javascript

[AlexChadwickP]

Feature request

Describe the solution you'd like

When applying the supabase-community/svelte-supabase svelte add, it should be able to identify whether the project is using JS or TS, and create the lib/db.{ts|js} accordingly.

Describe alternatives you've considered

Technically we could just rename the file, it's not a massive chore but it would be sweet if it could be done automatically.