Add support period for Turris devices
This could be part of Turris OS version table from https://docs.turris.cz/basics/tos_versions/
This should help meet the following mandatory requirements for Tier 1 defined by CSA Singapore's Cybersecurity Labeling Scheme
- 5.3-13:The manufacturer shall publish, in an accessible way that is clear and transparent to the user, the defined support period.
Related to https://gitlab.nic.cz/turris/biz/singapore-certification/-/issues/1