template upload.

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

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

Redner varlist substitute get_redner_tmpl_keys func for
retrieving redner templates variables.

Rename "Template" -> "Odoo Template"
Rename "Template + Deserialize" -> "Odoo Template + Eval"

Rework on relations converters
Remove deprecated field (ie: deserialize)
Use converter on mail template model
Updated the french translations

Added a custom converter image

This method will be called in ``_render_template`` method to
add additional variables.

Reviewed ir.actions.report and mail template models; Replace
obsolete methode "render_template" by "_render_template"

Retrieve the list of variables present in the template.

Only required for mustache/handlebars template engines.

Following the new functionality (template engine with od+mustache),
this change aims to improve:

* the creation of redner template
* the update of redner template

- Bump module version to 13.0.1.0.0
- Remove all the decorators @api.multi, @api.one and so on...
- Update translation files

Render HTML to PDF with weasyprint:

- Use substitution variables in ir.actions.report model
- Send paperformat field info to rednerd when generating a new report PDF
- Refactoring code

Add rednerd template management API to let the user save templates
for later use with the rendering api:

- POST: /api/v1/template/{account}
- PUT: /api/v1/template/{account}/{name}
- DELELTE: /api/v1/template/{account}/{name}

Render a custom template:

- POST: /api/v1/render