appending Google docs and adding header and footer

In the current implementation, the adding of header and footer is done by making a copy of an existing template doc which has the required header and footer, and then appending the required contents inside it. 

Unfortunately, with the (slow) template method, Google Apps script seems to have difficulty with importing more than 2-3 chapters at a time, where each chapter consists of around 10-15 Google Docs which need to be concatenated. Each chapter takes 5 to 10 minutes, and we reach the limits of processing time + parsecsv's max char limit. 

https://tanaikech.github.io/2019/08/28/benchmark-importing-csv-data-to-spreadsheet-using-google-apps-script/

The appending-Google-doc code is from 
https://stackoverflow.com/questions/51252160/can-i-copy-the-contents-of-one-doc-to-a-specific-spot-in-another-doc-google-ap