* Update website docs regarding ssh role allowed_extensions parameter
- Add note within the upgrading to 1.9.0 about behaviour change
- Prefix the important note block within the main documentation about
signed ssh certificates that it applies pre-vault 1.9
- Update api docs for the allowed_extensions parameter within the ssh
role parameter.
* Apply suggestions from code review
Co-authored-by: Loann Le <84412881+taoism4504@users.noreply.github.com>