* Prevent underscore character being used in 'name'.
* Restrict underscores in hostnames, not all names.
* Use hostname validator for node name.
* Allow underscore in hostname but warn once.
* Add renaming instructions link to warning.
* Point underscore warning to FAQ section
Co-authored-by: Otto Winter <otto@otto-winter.com>
Co-authored-by: Otto Winter <otto@otto-winter.com>