API Bulk update for users and groups

**Is your feature request related to a problem? Please describe.**
I integrated the Authentik API in one of our tools. In one use case I need to update a attribute of all users that have a certain value of that attribute and are in a defined group. In my test scenarios these are around 1000 users. At the moment I fetch each user, update the attribute value (so I don't overwrite the complete field) and update it via the API. Authentik breaks after some updates with the error:

```
{"error":"context canceled","event":"failed to proxy to backend","level":"warning","logger":"authentik.router","timestamp":"2024-07-31T07:18:21Z"}
```

**Describe the solution you'd like**
It would be nice to have a PUT route to update attribute values of all users / groups with a certain value for a defined attribute.

**Describe alternatives you've considered**
I considered doing it directly within the database via a SQL query. Something like

```
UPDATE authentik_core_user
set attributes['my_attribute'] = to_jsonb(15);
WHERE
attributes->>'my_attribute' = 14
```

**Additional context**
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