2020-07-17: initial release, cisco_trustsec_pac
2020-07-19: added cisco_trustsec_environment and cisco_trustsec_sxp_peer
2020-07-22: added wato for cisco_trustsec_pac, cisco_trustsec_environment and cisco_trustsec_sxp_peer
2020-07-23: improved wato, code cleanup, moved minor infotext to longoutput
2020-07-24: added cisco_trustsec_server, added alias and not found state to cisco_trustsec_sxp_peer
2021-08-01: rewritten for CMK 2.0
2022-11-30: WATO: fixed CheckParameterRulespecWithoutItem (from CheckParameterRulespecWithItem)
2023-04-12: refactoring cisco_trustsec_pac
            cisco_trustsec_pac: added wato option to configure monitoring state if PAC expired (default CRIT)
                                added expiration_time as perfdata
                                made checklevels for expiration_time work with negative time span
                                deprecated option expiration_levels, replaced by max_time_before_expire
2023-04-15: refactoring cisco_trustsec_environment, cisco_trustsec_server, cisco_trustsec_sxp_peer
            refactoring _get_snmp_date and _get_seconds_to_expiration
            cisco_trustsec_environment: removed default levels, added time to refresh as metrics
                                        discovery ignores now systems that have never downloaded the environment (CTS likely not active)
            cisco_trustsec_server: made monitoring states configurable (state_not_alive, state_not_provisioned, state_test_not_enabled)
                                   added support for IPv6 servers
            cisco_trustsec_sxp_peer: separated check_levels and metrics for SXP Peer Uptime to have scalars, changed name to sxp_uptime
                                     removed default levels for minuptime_levels
                                     added support for IPv6 SXP peers
2023-04-17: moved WATO/metrics file for ~/local/lib/checkm_mk/gui/plugins/..                                     
2023-06-07: cisco_trustsec_environment: modified, yield only download_status if environment cleared