Following Feed should include Lists updates (not just reading log)

### Feature Request

### Problem / Opportunity

When a subscriber follows other patrons, they expect to see updates from that patron. The updates today only include Reading Log actions.

It would be great if this activity feed also included items added to Lists.

https://openlibrary.org/query.json?query={%22type%22:%20%22/type/list%22,%20%22key~%22:%22/people/ScarTissue/*%22,%20%22*%22:null,%20%22sort%22:%20%22-last_modified%22}

The blocker or challenge right now is Reading Logs can be queried a single time for many usernames, whereas we must first get all of the recently modified lists for a single user (making it somewhat untenable right now).

Some platforms employ a "Fanout on write" policy, where events across types are included in this table, and we basically just query for patron names in this table that are being followed.

Perhaps a `patron_events` which gets pushed to any time (user_key, item_key, metatype)
e.g. `(@scarTissue, `@mekBot`, {"follow"})` or `(@scarTissue, /lists/scarTissue/OL12312L, {"list-add": "/books/OL123M"})`

Periodically truncate table, only 1 month of history?

## Downsides or Risks

Yet another table, we would have to add anonymization support, update stale IDs (even harder for json types)

### Proposal

### Evaluation

For now we've decided that we won't implement this.

### Breakdown

### Related files

Refer to [this map of common Endpoints](https://github.com/internetarchive/openlibrary/wiki/Endpoints):
*

### Requirements Checklist
Checklist of requirements that need to be satisfied in order for this issue to be closed:
* [ ]

### Stakeholders

*

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