Support Nextcloud 30.0.0

This versioned release has been tested to be compatible up to Nextcloud v30.0.0.

This release introduces the following changes:

• add support for metadata format version 2.0 (#51)
• add skip_files tests (#53)
• update CHANGELOG.md (#54)
• increase decryption block size (#55)
• improve config type checks (#58)
• add Nextcloud30 test (#60)