template upload.

converter backport in 2021-06.
In particular, add "HTML + mustache" / "MJML + mustache" instead of just "mustache".

add /api/v1 in the code.

Request contents only logged at debug level.

Add constraint on attachment field

Note that it is normally expected that when printing a report from an object,
the created document is saved as an attachment to the object
if the field "Save as attachment prefix" is filled in.

Problem:
This does not work for redner reports (works for QWEB and worked for py3o).

Updated the NEWS.rst file
Version update in dunder file dunder