Configuring custom JRE undocumented for REST API

While configuring a custom JRE path is documented for configuring nodes in the UI[1] and CLI[2], it is missing from the REST api documentation[3]. This will probably need to be re-titled as it currently indicates that the api is used to set storage paths, but while this is a node-specific path, it is not storage related.

[1] - https://docs.couchbase.com/server/current/install/init-setup.html#configure-couchbase-server
[2] - https://docs.couchbase.com/server/current/cli/cbcli/couchbase-cli-node-init.html
[3] - https://docs.couchbase.com/server/current/rest-api/rest-node-index-path.html