feat: add generic HTTP LLM provider support

[shiningstone23]

Add a flexible provider that can connect to any HTTP-based LLM API using configuration-driven request/response mapping.

Features:

• JSON configuration schema for defining custom LLM API integrations
• Template variable substitution for requests (${VAR}, ${VAR:number}, etc.)
• JSONPath-based response parsing ($.content, $.error, etc.)
• Multiple authentication methods (Bearer, Header, Basic, Query)
• SSE/Chunked streaming support
• Tool injection for LLMs without native tool calling support
• Skip SSL verification option for self-signed certificates
• Custom environment variable prefix support

Usage:

1. Create a JSON config file in ~/.config/goose/custom_providers/
2. Define endpoint, auth, request template, and response parsing
3. Run goose configure to set up the provider

Example config: crates/goose/examples/generic_http_provider.json

Summary

Type of Change

• Feature
• Bug fix
• Refactor / Code quality
• Performance improvement
• Documentation
• Tests
• Security fix
• Build / Release
• Other (specify below)

AI Assistance

• This PR was created or reviewed with AI assistance

Testing

Related Issues

Relates to #ISSUE_ID
Discussion: LINK (if any)

Screenshots/Demos (for UX changes)

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After:

[DOsinga]

thanks for the contribution. what is the advantage over this over the current approach of custom providers? I see this has more fields, but can't we just add those to custom providers, rather than ending up with what is effectively two different json formats to specify a generic provider? haven't looked closely at the code so I might be missing something here of course.