gmail-to-drive-by-labels does not provide a 'Rebuild Doc' option

[don-petry]

When using the gmail-to-drive-by-labels functionality, there is no method to recreate/rebuild the Google Doc which is populated with email bodies. This creates a problem when the logic for building the body changes.

For example

1. If changes are made to the 'getCleanBody' there is no way to recreate the document with the improved filtering.
2. When features like gmail-to-drive-by-labels adds new content to the bottom rather than top of document #22 are implemented they cannot be retroactively applied

Goal: Provide a mechanism to reset the Google Doc and reprocess all labelled emails to rebuild the document.

Technical Requirements: Due to GAS script timeouts, a method must be used to ensure all labelled emails are reprocessed.

Consider using this approach to provide a reset mechanism:

1. Clear the configured document bodies
2. Switch all configured labels from 'archived' to not
3. Allow the normal synchronization process to repopulate and rearchive the emails

[don-petry]

Resolved and tested. Works great!