Heroku integration

[abernicchia-heroku]

I helped with updating that part on v11 but now I see it has dissapeared from v12 and the repo is now archived (since Jan 2024).

I do assume it still works without any changes, so wondering why removing it.

Please, let me know if I can help with reinstating it.

Thanks

[wolfgangwalther]

It was removed in PostgREST/postgrest-docs#735.