RATIONALE
Improve usage of composer in comment or email mode: support batch-posting in
comment, support more configuration from templates, improve global model.
SPECIFICATIONS
Remove 'is_log' field on mail composer. Indeed its usage can be globally
replaced by using the 'note' subtype when posting. It is now better matching
the result of using the log a note mode of chatter.
Posting with a False subtype_id already automatically converts it into a
note subtype in 'message_post'. It is now done directly at composer level
to lessen magic and have more control on final output.
In case of outgoing emails subtype has no usage, as notification process is
not called. It is therefore forced to False when creating the mail records.
Task-3035101 (Mail: Support batch-posting from composer)
Part-of: odoo/odoo#99482
Thibault Delavallée
629ba0c392