Release 2.1.1

[kelson42]

• Secure the CI is green on git main
• Update the Changelog
• Check if this new release use latest version of libkiwix and libzim
• Update version
• Close current milestone and create new one incrementaly (a priori a minor version)
• Create a tag on git
• Secure new version is published on Maven Central
• Update the Github release with the Changelog
• Create new empty entry in Changelog (placeholder for future entries)
• Advertise this new version