docs: cc_users_groups: add more explicit docs on impact of omission of "- default" user on a system

[ubuntu-server-builder]

This bug was originally filed in Launchpad as LP: #1943275

Launchpad details

affected_projects = []
assignee = None
assignee_name = None
date_closed = None
date_created = 2021-09-10T17:34:53.078840+00:00
date_fix_committed = None
date_fix_released = None
id = 1943275
importance = low
is_complete = False
lp_url = https://bugs.launchpad.net/cloud-init/+bug/1943275
milestone = None
owner = chad.smith
owner_name = Chad Smith
private = False
status = triaged
submitter = chad.smith
submitter_name = Chad Smith
tags = ['docs']
duplicates = []

Launchpad user Chad Smith(chad.smith) wrote on 2021-09-10T17:34:53.078840+00:00

https://cloudinit.readthedocs.io/en/latest/topics/modules.html#users-and-groups should have a more visible note explaing the affect of omitting "- default" as this is a fairly frequent accidental side-effect for user-config containing "users:" directives.