Add Auto Tier Managed Setting

[rwoll]

Track VS Code support for the model-tier managed settings design discussed in https://github.com/github/agent-control-plane/issues/1578.

Setting names and schema are still being finalized upstream.

cc: Harald Kirschner (@digitarald) Frank Salmick (@Strombon)

[rwoll]

SteVen Batten (@sbatten) Logan Ramos (@lramos15) - once the schema of the settings are finalized, I may ask for the Model Picker team :P to help implement as the Model Picker is currently going through a lot of iteration.

Thanks!