Add an option to exclude PDF attachment in email

[robroc]

By default, FOIAmail adds a PDF attachment of the request text as a PDF named records-request.pdf (Line 281 in compose.py) It would be good to turn off this option in the congif.yaml file, and also to be able to rename the PDF if we choose to include it.

[brandonrobertz]

Markdown is used only for preparing the PDF version of your request. So essentially, using markdown is only for those wanting to attach a PDF of their request. If you want to just send a basic message without attachments, right now your only option is to use the docx message.

[robroc]

That's helpful to know, thank you. I will suggest an addition of this information to the docs with a PR.