Private Google Spreadsheet support

Up until now to connect your Google Sheets spreadsheet to sheet2api you would have to make your spreadsheet public to the entire world.

This is fine if you keep your spreadsheet link to yourself but not ideal if you share it within your company and it contains private information.

I could see from server logs this was putting off some customers from using the service. So I finally figured out how to make a Google Sheet to able to connect to our service, but remain totally private to the outside world 👍.

I also updated the documentation with a super simple video on how to do it https://sheet2api.com/documentation/#sharing

Do you have any ideas for what spreadsheet features I should build next? If so, feel free to comment below.