[FEATURE] Add Modelsell as an OpenAI-compatible provider integration #6675

Feature Description

Add Modelsell as a named OpenAI-compatible model provider integration in Flowise.

Modelsell provides a unified OpenAI-compatible endpoint:

• API base: https://modelsell.com/v1
• Chat Completions: POST /v1/chat/completions
• Model discovery: GET /v1/models
• Authentication: Bearer API key
• API key page: https://modelsell.com/console/token
• Documentation: https://modelsell.com/docs/api-reference

The integration should reuse Flowise's existing OpenAI-compatible model path and fetch models dynamically from /v1/models instead of maintaining a hardcoded model list.

Feature Category

Integration

Problem Statement

Modelsell can be configured manually through an OpenAI-compatible/custom model node today, but users need to know and repeatedly enter the correct endpoint, key location, and model IDs. This makes the provider harder to discover and introduces avoidable configuration errors across flows.

Proposed Solution

Add a focused Modelsell provider preset or model component that:

1. Defaults the base URL to https://modelsell.com/v1.
2. Uses bearer API-key authentication.
3. Loads available models from GET /v1/models.
4. Reuses the existing OpenAI Chat Completions implementation without provider-specific request transformations.
5. Includes links to the Modelsell API key page and documentation.

If a dedicated component is not preferred for OpenAI-compatible providers, a documented preset/example using the existing custom OpenAI component would still reduce setup friction. I can contribute the implementation in the form preferred by the maintainers.

Mockups or References

• Website: https://modelsell.com
• API keys: https://modelsell.com/console/token
• API documentation: https://modelsell.com/docs/api-reference
• Models endpoint: https://modelsell.com/v1/models

Additional Context

The first contribution can stay limited to Chat Completions and dynamic model discovery. It does not need a hardcoded catalog or a new transport layer.

Disclosure: I represent Modelsell.