Handle error cases in `sync_transactions`

https://github.com/evanphilipsmith/gsheets-plaid/blob/fba22d39d019183bdd4cb72895646be22bffff8f/gsheets_plaid/sync.py#L271-L276

We should handle cases when the parameters contain invalid credentials/tokens. Consider the following cases for example:
 - Google credentials are invalid
 - Plaid credentials are invalid
 - Spreadsheet ID is invalid
 - Access tokens are invalid