Release 2.1.0

[kelson42]

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