Update contributing docs to reflect JDK 11 (#40955)
Update contributing docs to reflect JDK 11 (#40955)

This commit updates the contributing docs in reflection of the fact that
the minimum JDK for the master branch (Elasticsearch 8.0.0) is JDK 11.
scorpionvicky/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,coding0011/elasticsearch,scorpionvicky/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,HonzaKral/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,HonzaKral/elasticsearch,scorpionvicky/elasticsearch