feat(core): improved logging / renames / new exports (#6085)
- Cleans up logging. Logs are now color-coded, added more debug logs, and errors can include some simple metadata (like provider id) to know which provider caused an issue.
- All errors are exposed via `@auth/core/errors`. Each error has a URL like: https://errors.authjs.dev#errorcode in the terminal, which points to the documentation explaining the problem in detail, suggesting a fix.
- Added a bunch of documentation that autogenerates the pages under https://authjs.dev/reference/core/modules/main
- Renames `AuthHandler` to `Auth` and `AuthOptions` to `AuthConfig`
- Throwing an error in `signIn` callback will now be caught as a general error and will redirect to `/error?error=Configuration`. If the callback returns `false`, it will redirect to `/error?error=AccessDenied`.
