Only show available flow types on flow triggers

What does this MR do and why?

• Queries flows if ai_catalog_flows is on
• Queries third_party_flows if ai_catalog_third_party_flows is on
• If both FFs are off
  • Skips query
  • Does not show radio button selection
  • Defaults to config file path mode

I have considered adding global_ai_catalog checks as well, but decided against it for some reasons. Let me know if you have questions.

Screenshots or screen recordings

Both off	ai_catalog_flows on	ai_catalog_third_party_flows on	Both on

How to set up and validate locally

1. Enable the feature flag: echo "Feature.enable(:ai_flow_triggers)" | rails c
2. Go to http://gdk.test:3000/gitlab-duo/test/-/automate/flow-triggers
3. Click on Create new flow trigger
4. Test out the feature flags listed top of this MR description

MR acceptance checklist

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