Add api_versions property to Instance entity. (#484)

This property will be available starting with Mastodon v4.3.0 as information about the API version offered by a Mastodon server.

See #483.

bigbone/src/main/kotlin/social/bigbone/api/entity/Instance.kt

@@ -69,6 +69,12 @@ data class Instance(
     @SerialName("registrations")
     val registrations: Registrations = Registrations(),
 
+    /**
+     * Information about which version of the API is implemented by this server.
+     */
+    @SerialName("api_versions")
+    val apiVersions: ApiVersions = ApiVersions(),
+
     /**
      * Hints related to contacting a representative of the website.
      */
@@ -353,6 +359,19 @@ data class Instance(
         val message: String? = null
     )
 
+    /**
+     * Information about which version of the API is implemented by this server.
+     */
+    @Serializable
+    data class ApiVersions(
+        /**
+         * API version number that this server implements. Starting from Mastodon v4.3.0,
+         * API changes will come with a version number, which clients can check against this value.
+         */
+        @SerialName("mastodon")
+        val mastodon: Int = 0,
+    )
+
     /**
      * Hints related to contacting a representative of the website.
      */