Provide a pure read only mode for DocumentNodeStore

Currently whenever an instance of DocumentNodeStore gets created it would make an entry to cluster collection and start the background read and write operations. Would also configured a last rev fixer etc

For safer tooling it would be required to have a mode where DocumentNodeStore can be configured to run only in a readOnly mode. In this mode

• No entry to be made in cluster collection
• No background write task scheduled
• No last rev recovery enabled
• In addition an option to also forcefully disable any explicit writes

This would allows the user a confidence that any tooling (oak-run) based would not leave any sort of side effect on the running system