Get secret with specific version ID

Currently, the only way to retrieve a secret is by its ID with `SecretCache.getSecretString(secretId)`. There is no way to get a specific _version_ of a secret using its ID and versionId. One can build a `SecretCacheConfiguration` object and call `setVersionStage`, then pass that configuration to a `SecretCache` constructor; however, this still only allows retrieving a specific version of a secret by its Id and _stage_, and would require using the same stage for all secrets (unless constructing separate caches). It would be nice if `getSecretString` took an optional `versionId` string, so that we could use specific versionIds and not just version stages.

Empieza trazando SecretCache.getSecretString(secretId) y la ruta de SecretCacheConfiguration.setVersionStage mencionada en el issue. Comprueba cómo el constructor de la caché recupera las versiones y, después, verifica que un versionId opcional pueda seleccionar una versión del secreto independientemente de las stages compartidas.

Escrito por el modelo de indexación a partir del texto del issue.