Improve API references by adding documentation URLs for each method

[ja7ad]

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

// 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)