Adding the correct DATABASE_URI for all db based in the credentials.uri [fixes #51427121]

- Removed the extra database.yml write as this is done by the buildpack
- Only used the uri field in the crententials as this is now guranteed by the services team
- Use the scheme from the uri and convert it to Rails Adapter acceptable names
- If no URI is present presume its not a relational DB. This maybe faulty but we dont yet have tags to check this properly.