Codesandbox-client: feat: improve error message when importing github repo

[manniL]

🌈 Feature

Hey all! Just tried to import my GH repo and a cryptic error occurred

After a while, I realized that my package.json had a trailing comma and was invalid (ref).

Unfortunately, the error message only partly helps with recognizing this error.

:heavy_check_mark: Invalid JSON
:x: Position 315 (if you put all on one line maybe?)
:x: Reference to package.json

I'd love to see a more detailed error message, however, this is a less common error I think :man_shrugging:

[SaraVieira]

All the messages around importing and committing from Github repos need to be improved :(

[SaraVieira]

Better late than ever but we do have better error messages now and we also have waaay fewer error messages because a lot has been fixed 🎉