2.0.x branch & new release supporting PHP 8.x

Problem/Motivation

The library we're using for calendar generation ( eluceo/ical → ) has a new version (2.0.x) that is a complete rewrite and not backwards compatible.

It has also dropped support for PHP Versions 7.3 and older.

Based on library's the upgrade guide we might not need to change anything on this module's code.

Proposed resolution

This seems like it's a needed version to support PHP 8.0 and beyond, so we will need to update the library for the future.

We cannot just upgrade the library in the existing branch, because it doesn't support PHP Versions 7.3 and older, so a new branch/version of the module should be created.

Remaining tasks

• Create a new branch
• Update library to 2.0.x & test if everything works fine.
• (Not sure) update composer.json for PHP version requirements.
• Create a release for this new version, marking it as recommended
• Update module's page:
  • Note PHP Version requirements for each release.
  • Upgrade Path 8.x-1.x ->2.0.x

Notice: This should be done after we have a stable release, so I'm marking this issue as postponed.