feat: add API key support for TEI reranker

[cblh]

fixes: #2741

Description

This change adds API key support for the TEI reranker. Here are the key changes:

1. In the reranker implementation:

   export class HuggingFaceTEIReranker implements Reranker {
   // ... existing code ...
   
   // Add apiKey to params
   constructor(
   private params: {
     apiBase?: string;
     truncate?: boolean;
     truncation_direction?: string;
     apiKey?: string;  // New parameter
   },
   ) {}
   
   async rerank(query: string, documents: Document[]): Promise<Document[]> {
   // ... existing code ...
   
   const headers: Record<string, string> = {
     "Content-Type": "application/json",
   };
   
   if (this.params.apiKey) {
     headers["Authorization"] = `Bearer ${this.params.apiKey}`;
   }
   
   const resp = await fetch(new URL("rerank", apiBase), {
     method: "POST",
     headers,  // Updated headers object
     // ... rest of existing code ...
   });
   // ... existing code ...
   }
   }

2. The schema files and documentation have been updated to include the new apiKey parameter in the configuration options for the TEI reranker.

Checklist

• [x] The base branch of this PR is dev, rather than main
• [x] The relevant docs, if any, have been updated or created

Screenshots

[ For visual changes, include screenshots. ]

Testing

The changes allow users to authenticate with the TEI API by providing an API key in their configuration. The key is sent in the Authorization header using Bearer token authentication.