Make metrics available while node is adapting to reserve-capacity-doubling change

[crtahlin]

Summary

As one changes reserve-capacity-doubling in the bee.yaml file and restarts the Bee, there can be a long period of no information via the APIs (getting code 503) and the /metrics endpoint (which only returns some basic stats).

There should be more information available, for the user to be aware of what is happening and possibly, how long it will last.

Motivation

After changing the reserve-capacity-doubling and restarting, the user should have some insights into the status of the node: is it doing what it is supposed to, what is happening, how long to wait until the node will again be usable?

Implementation

No ideas, but I guess some of the endpoints and /metrics could be available even before the node is fully fuctional again. Like the /status endpoint should show that it is in process of ... ??? (It says that node is syncing, but it is probably actually garbage collecting and purging?)

Drawbacks