This commit adds the `data_frozen` node role as part of the formalization of data tiers. It also
adds the `"frozen"` phase to ILM, currently allowing the same actions as the existing cold phase.
The frozen phase is intended to be used for data even less frequently searched than the cold phase,
and will eventually be loosely tied to data using partial searchable snapshots (as oppposed to full
searchable snapshots in the cold phase).
Relates to #60848
3f9f007545