Google Sheets document ID for generating the view link
Returns void
Throws
Will throw an error if the HTML template file cannot be read
Throws
Will throw an error if the output file cannot be written
Remarks
The function expects an HTML template file to exist at src/static/email-template.html.
The template should contain placeholders like {{EXPENSES_TOTAL}}, {{NET_INCOME}}, etc.
Creates an HTML email body with financial report data and saves it to a file.
This function generates a comprehensive financial report email by: