Use multiple PGP/MIME attachments for text snippets and OpenPGP public key included in Whisperback reports

Some of us thought it would be easier to process Whisperback reports if the log files where sent in separate PGP/MIME attachments. It is sometimes tricky to find the right piece of information in the middle of all the rest.

Subtasks

#6184 (closed)
#8513 (closed)
#8514 (closed)
#8722

Related issues

Related to #15470 (closed)

Original created by @intrigeri on 6183 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information