Improve API references by adding documentation URLs for each method

Description

To improve the documentation of each API method, we should add a corresponding documentation URL. This will help clients better understand the APIs when using them in projects.

Reference: https://www.meilisearch.com/docs/reference/api/overview

Important note: Only add API references to interface methods.

Example

<img width="642" height="148" alt="Image" src="https://github.com/user-attachments/assets/ee82c1ce-6583-4161-8971-bc5ca0ed00cd" />

// CreateIndex creates a new index.
//
// docs: https://www.meilisearch.com/docs/reference/api/indexes#create-an-index
CreateIndex(config *IndexConfig) (*TaskInfo, error)

// CreateIndexWithContext creates a new index with a context for cancellation.
//
// docs: https://www.meilisearch.com/docs/reference/api/indexes#create-an-index
CreateIndexWithContext(ctx context.Context, config *IndexConfig) (*TaskInfo, error)