Move PMs page to Resources menu?

[crandmck]

Per discussion in #993, the PMs page should probably be under Resources instead of Advanced topics, since it discusses 3rd-party modules/solutions.

I wonder if it also makes sense to combine the content of Process Managers and the relatively new page Health checks and graceful shutdown, which are related topics?

[dougwilson]

Really, I could see it either way. I think that (and this is just thinking out loud) it would make sense if we could at some point have in the Advanced topics section generic information about process managers, health checks, graceful shutdown, etc. Then those would point to the third party solutions that are in the Resources section.

[crandmck]

Irrelevant with landing https://github.com/expressjs/expressjs.com/pull/1484.