Unfortunately,coderd validation errors don't return the reason why the validation failed, leading to confusing (almost useless) error messages when creating templates, groups or users with invalid names via the provider.

The changes oncoderd/httpapi to resolve this are non-trivial, as thestruct validation library we use doesn't appear to support attaching an error reason to a field validator function.

Instead, we'll translate the string validation functions and regex fromcoderd/httpapi/name.go.