kvserver,cli,roachtest,sql: introduce a fully decommissioned bit

Lauren Hirata Singh (lnhsingh) commented:

PR: https://github.com/cockroachdb/cockroach/pull/50329

From release notes:
> Introduced a `membership` column to the output generated by `cockroach node status --decommission`. It should be used in favor of the `is_decommissioning` column going forward. [#50329][#50329] {% comment %}doc{% endcomment %}

Jira Issue: DOC-677