Add quartz-2.2.3 documentation

[sumbach]

• Fixes broken link to /documentation/quartz-2.2.3/index.html
• Updates left sidebar to point to 2.2.3 (latest 2.2.x release)

[jhouserizer]

Hello! Thank you very much for your contribution and interest in helping improve the Quartz community.

After a period of dormancy, the Quartz project is back under steady maintenance by multiple volunteers, who are working to once again handle contributions such as yours.

We notice that your contribution was made without use of the DCO feature (the sign-off feature on commits via the -s option). Can you please update your PR with commits that use the -s option, agreeing to assign copyright ownership and other terms as described at the contributor agreement referenced here: https://github.com/quartz-scheduler/contributing/blob/main/CONTRIBUTING.md

You can easily add signoff to your previous commits by running (on your PR branch):

git commit --amend --signoff --no-edit 
git push -f

Or (for multiple commits):

# change 5 to the number of commits
git rebase HEAD~5 --signoff
git push -f