Ingester behavior when disk is full

[fulmicoton]

Currently, ingester may end up accepting persist request when their disk is full.
If the OS buffer is not full, no error might be returned.

We need to poll-check for the disk usage, and change the behavior of quickwit when it goes above
a threshold.

The behavior is yet to be decided. Probably, the closest thing is decommissionning: close all shards and not accept the creation of new shards. In addition, it might not be possible to run indexing/merge pipelines; which could really make the control plane's task hard.