Be able to inject which "model" to use for each Agent

[cicorias]

Ideally per workspace -- keeping it consistent within a team/project - be able to choose which model for each agent --

i.e some models are better at some tasks vs others...

[WilliamBerryiii]

@agreaves-ms and I have talked this through a few times and still feel, given the wide breadth of devs using different tiers of models, that we'd steer away from explicitly calling it out. I use Haiku on my personal projects because I don't pay for GHCP pro ... and I'd prefer not to have to change each model file. The real thing may be to prod the VSCode extension team for GHCP to allow us to have some buckets of work types and be able to assign default or suggested models for a given task.