sentinel packages: i_agree_with_eula option check and sentinel config

We need to have configuration option that user signals with that he agreed with our eula.

• create common shell library to check for EULA approval !287 (merged)
• add check to init scripts and cron scripts for that (tools should not start nor run without EULA) (https://gitlab.labs.nic.cz/turris/sentinel/nikola/-/merge_requests/15)
• implement script to kick on sentinel when EULA is approved (manual/Foris call) !397 (merged)
• make that part of sentinel-proxy package !397 (merged)

Reference issue https://gitlab.labs.nic.cz/turris/turris-os-packages/issues/493

This is requires as well for migration so users are migrated from ucollect with enabled Sentinel as initial Sentinel EULA is the same one as for uCollect.