Allow task list to be specified via preset? If not, document.

### Feature description

https://worker.graphile.org/docs/config#worker-options doesn't indicate a task list. If this is deliberate, document why it's not there. If it's not deliberate, consider adding it.

### Motivating example

https://discordapp.com/channels/489127045289476126/697954986461495346/1211476431113027705

### Breaking changes

None

### Supporting development

I [tick all that apply]:

- [x] am Benjie

Start with the worker options documentation at https://worker.graphile.org/docs/config#worker-options and review the motivating Discord discussion. Determine whether a task list should be supported in presets; done means either documenting why it is excluded or adding the support and updating the configuration documentation.

Written by the indexing model from the issue text.