[Refactor] Change the signature of methods of MetadataService

[mercyblitz]

Marking sure the stable ordered collection for Dubbo service URLs, thus it's required to change the signature of methods in MetadataService

Before :

    /**
     * Get the list of String that presents the specified Dubbo exported {@link URL urls} by the
     * <code>serviceInterface</code>, <code>group</code>, <code>version</code> and <code>protocol</code>
     *
     * @param serviceInterface The class name of Dubbo service interface
     * @param group            the Dubbo Service Group (optional)
     * @param version          the Dubbo Service Version (optional)
     * @param protocol         the Dubbo Service Protocol (optional)
     * @return the non-null read-only {@link List} of {@link URL#toFullString() strings} presenting the {@link URL URLs}
     * @see URL#toFullString()
     */
    List<String> getExportedURLs(String serviceInterface, String group, String version, String protocol);

After :

    /**
     * Get the {@link SortedSet sorted set} of String that presents the specified Dubbo exported {@link URL urls} by the
     * <code>serviceInterface</code>, <code>group</code> and <code>version</code>
     *
     * @param serviceInterface The class name of Dubbo service interface
     * @param group            the Dubbo Service Group (optional)
     * @param version          the Dubbo Service Version (optional)
     * @return the non-null read-only {@link SortedSet sorted set} of {@link URL#toFullString() strings} presenting the {@link URL URLs}
     * @see #toSortedStrings(Stream)
     * @see URL#toFullString()
     */
    default SortedSet<String> getExportedURLs(String serviceInterface, String group, String version) {
        return getExportedURLs(serviceInterface, group, version, null);
    }