cluster: overriding inspector port

Added an option to override inspector port for workers using
`settings.inspectPort` will override default port incrementing behavior.
Also, using this option allows to set 0 port for the whole cluster.

PR-URL: https://github.com/nodejs/node/pull/14140
Fixes: https://github.com/nodejs/node/issues/8495
Fixes: https://github.com/nodejs/node/issues/12941
Refs: https://github.com/nodejs/node/pull/9659
Refs: https://github.com/nodejs/node/pull/13761


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>