Implemented the Services and Database GET endpoints (#2)

This PR contains the work done to include the define the information sections of the `OpenAPI` specification document and all the `GET` endpoints of the _Service_ and _Database_ categories.

The following endpoints have been defined in the document, and also tested manually with `Swift`:
* GET `/`
* GET `/artists/{artist_id}`
* GET `/artists/{artist_id}/releases`
* GET `/labels/{label_id}`
* GET `/labels/{label_id}/releases`
* GET `/masters/{master_id}`
* GET `/masters/{master_id}/versions`
* GET `/releases/{release_id}`
* GET `/releases/{release_id}/rating`
* GET `/releases/{release_id}/rating/{username}`
* GET `/releases/{release_id}/stats`
* GET `/database/search`

In addition, a first version of the _Github Pages_ documentation has been generated from the `DocC` documentation catalog, and the generated Swift code from the `openapi.yaml` file.

Reviewed-on: #2
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Sources/DiscogsService/openapi-generator-config.yaml

@@ -0,0 +1,19 @@
+## ===----------------------------------------------------------------------===
+## 
+## This source file is part of the Discogs Service open source project
+## 
+## Copyright (c) 2025 Röck+Cöde VoF. and the Discogs Service project authors
+## Licensed under Apache license v2.0
+## 
+## See LICENSE for license information
+## See CONTRIBUTORS for the list of Discogs Service project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+## 
+## ===----------------------------------------------------------------------===
+                    
+generate:
+    - types
+    - client
+namingStrategy: defensive
+accessModifier: public