Display additional AI provider plugins on Connectors page (alongside default Anthropic, Google, and OpenAI ones)

Description

Enable developers, agencies, and hosts to pre-configure AI providers that will be automatically recognized by the plugin. This supports a “progressive provider selection” approach (where existing providers are utilized and only presents provider configuration needs if no applicable provider has been configured) and reduces the need for manual setup.

Goals

• Define a configuration system (using constants, filters, or configuration files) to allow pre-configured providers.
• Ensure the system is modular so each feature can independently detect and use available providers.
• When a valid pre-configured provider exists, the UI for provider selection should be hidden.
• Document the configuration process with clear examples for hosts and network administrators.
• Align with the encapsulated feature architecture so each feature can extend or override provider handling if needed.

Acceptance Criteria

• Plugin detects and auto-selects any pre-configured providers.
• Provider selection UI is suppressed when configuration is detected.
• Features automatically inherit available provider connections.
• Developer documentation includes at least one working example.