Add support for managing attachments

Add a new manager for attachment records (`ir.attachment`) in Odoo.

These are intended to be used for uploading/downloading attachments to/from invoices.
Invoice attachments will then be attached to invoice emails sent out to customers.

The contents of the attachments won't be fetched when querying them from Odoo by default;
instead it is intended that the separate `download` method be used to download the attachment
contents separately. An `upload` method is also available, to provide an easier to use interface
for uploading attachments.

Author: Callum Dickinson

_typos.toml

@@ -0,0 +1,2 @@
+[default.extend-words]
+datas = "datas"

changelog.d/11.added.md

@@ -0,0 +1 @@
+Add support for managing attachments

docs/managers/account-move.md

@@ -177,6 +177,40 @@ is_move_sent: bool
 
 Whether or not the account move (invoice) has been sent.
 
+### `message_main_attachment_id`
+
+```python
+message_main_attachment_id: int | None
+```
+
+The ID of the main [attachment](attachment.md) on the account move (invoice),
+if there is one.
+
+*Added in version 0.2.0.*
+
+### `message_main_attachment_name`
+
+```python
+message_main_attachment_name: str | None
+```
+
+The name of the main [attachment](attachment.md) on the account move (invoice),
+if there is one.
+
+*Added in version 0.2.0.*
+
+### `message_main_attachment`
+
+```python
+message_main_attachment: Attachment | None
+```
+The main [attachment](attachment.md) on the account move (invoice), if there is one.
+
+This fetches the full record from Odoo once,
+and caches it for subsequent accesses.
+
+*Added in version 0.2.0.*
+
 ### `move_type`
 
 ```python