Store history of publications in workspace collection's metadata

[leplatrem]

Currently, if we want to track the history of publications of a certain collection, we have to either:

• query our logs
• query the bucket history (example in telescope)

This is not impossible to do, but what if we would store in the workspace collection metadata right away (when we set last_signature_date and last_signature_by).

{
  "latest_approvals": [
     {"date": "...", "by": "...", "timestamp": 123456, "changes": {"created": 0, "updated": 3, "deleted": 0}},
     {"date": "...", "by": "...", "timestamp": 12345, "changes": {"created": 0, "updated": 1, "deleted": 0}},
     {"date": "...", "by": "...", "timestamp": 1234, "changes": {"created": 1, "updated": 0, "deleted": 3}},
     {"date": "...", "by": "...", "timestamp": 123, "changes": {"created": 2, "updated": 0, "deleted": 0}},
  ]
}

• It would be trivial to implement
• This would allow us to easily show this trail in the UI
• We could use these timestamps in the UI as comparison points to support Admin UI: improve history browsing for individual records #949
• The workspace metadata is not consumed by clients, so we don't care about its size (plus repetitive data with gzip is fine)
• We could limit to a few hundreds for collection with frequent updates

┆Issue is synchronized with this Jira Task