docs(nimbus): Add rollout mermaid diagrams

[RJAK11]

Because

• we need to add Mermaid diagrams reflecting the new rollout-specific state machine

This commit

• adds the Mermaid diagrams for rollouts
• updates timeout flows to return to idle after timeout

Fixes #16153

[RJAK11]

During our diagram review meeting and local testing, we found that when a Remote Settings review times out, the owner has to request review again. Because of that, we updated the timeout flows to reflect this behavior. We may need to make the same kind of update to the experiment diagrams as well.

[yashikakhurana]

Also worth noting that @freshstrangemusic mentioned that rollout pause only works for the labs, what will happen for non labs rollouts, will it keep the pause behaviour as expected that means users who are already enrolled will still enrolled, but no users will be enrolled 👀
cc @jaredlockhart and @freshstrangemusic

[RJAK11]

I have switched all uses of <none> for None, changed all the Enable cases to have Phase Next: Phase X+1, and added the two cases for enabling with no next phase. Let me know if something seems off! 🙏🏼

[jaredlockhart]

Alright!! Looks great to me. Thank you so much for doing this @RJAK11. This will make implementation MUCH smoother and will act as a reference for a long time. Let's do it and then we can unblock #16097 🎉 🎉 🎉 🎉 🎉 🎉