Upgrade graphql servlet to 9.0.1 to fix content length issue

Merge pull request graphql-java-kickstart#301 from graphql-java-kicks…

…tart/feature/separate-graphql-tools-starter

Separate graphql tools starter

Merge branch 'upgrade_servlet_version'

Added websocket subscription metrics

Merge branch 'feature/graphql-12'

Merge pull request graphql-java-kickstart#237 from graphql-java-kicks…

…tart/feature/graphql-12

Upgrade to graphql-java 12.0

Bumped version to 5.7.3 in README

Prepared 5.7.1 version number

Bumped version number to 5.7.0 in README

Merge pull request graphql-java-kickstart#202 from graphql-java-kicks…

…tart/feature/batch-handler-update

Updated batch execution handling