Add release date for 4.6.1 to the website
Add release date for 4.6.1 to the website

Author: Enrico Olivelli <eolivelli@apache.org>

Reviewers: Sijie Guo <sijie@apache.org>

This closes #1080 from eolivelli/update-website-4.6.1

apache/bookkeeper,ivankelly/bookkeeper,sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,ivankelly/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,ivankelly/bookkeeper,apache/bookkeeper,sijie/bookkeeper