Create an Activity Pub example

[RachL]

Context

https://github.com/orgs/datafoodconsortium/discussions/18

Acceptance criteria

We want to create some example notifications using the Activity Pub protocol, to better understand how activity pub could be used in our case.

Criteria:

• we need to consider that users and platforms can be actors (some platforms have delegated rights from their users and can act on their behalf)
• other?

[lecoqlibre]

We should list and describe use cases for which notifications are needed. Maybe a task for you @RachL and @RaggedStaff?

[RachL]

@lecoqlibre Ah I thought we would only consider stock movements as a first step? Otherwise, each field update can be notified (it's what we do with the refresh button currently).