Fix default api_type for specific github copilot models

[joshbarrington]

closes: #2303

Some Github Copilot models require the /responses endpoint as opposed to /chat/completions.

These are not set by default, and so certain models will fail unless a custom agent config is set with api_type: openai_responses. This sets the default for these models as openai_responses.

@liketosweep

[joshbarrington]

@liketosweep can you also test this? I've actually ran out of Github Copliot credit 😆 .

[liketosweep]

Hey @joshbarrington, just saw @dgageot gave it the green light! I was getting ready to pull it down but ran out of time on my end tonight before logging off. Thrilled it got approved and is ready to merge though great fix.

[joshbarrington]

@dgageot I just realised it makes sense to call the function earlier inside applyModelDefaults to avoid returning early.

I'll push that change now