Previously, replica nodes were labeled with a `running` state. As a
result, our checks were based on nodes marked as `running` through
the `--running-[warning|critical]` options.
However, with the recent changes in Patroni 3.0.4, replica nodes now
carry a `streaming` state. This shift in terminology calls for an
adjustment in our approach. A new state, `healthy_member`, has been
introduced to encompass both `running` and `streaming` nodes.
Key Modifications:
* The existing `--running-[warning|critical]` option is now designated
as `--healthy-[warning|critical]`.
* Introduction of the `healthy_member` perfdata, which serves as the
reference point for the aforementioned options.
* Updates to documentation, help messages, and tests.