[Go] Improve model configuration

[MichaelDoyle]

From a UX standpoint it would be nice to do the following:

1. REQUEST If we can order the options so that important ones are up top. See JS for a consistent ordering. In JS we have "common" options that apply to all providers that end up towards the top, then model provider specific following from that.
2. REQUEST Have help text bubbles (needs field descriptions on the schema)
3. REQUEST Hide system instruction (its provided in messages instead)

There also seems to be an issue with "Tool config" for Gemini. There is some missing metadata somewhere that causes these "Nested object settings" defaults to display.

REQUEST Irrespective of that, though if possible, can these be 2 separate config options (function calling and retrieval)?.

For reference, here is Go vs TS