Werk #11152: cisco_vpn_sessions: extensions and refactoring

Building on werk #11150, this werk extends the monitoring of Cisco VPN sessions.

• The services corresponding to this check are renamed from "[session type] Sessions" to "VPN Sessions [session type]". This places them next to each other in the Checkmk GUI.
• In addition to the number of active sessions, the check now also reports peak values and cumulative values as well as the global system limit on the number of concurrent sessions.
• Besides the number of client, clientless and remote access sessions, the check now also monitors the number of LAN-to-LAN sessions, discovered as "IPsec L2L". For clarity, the service monitoring the number of remote access sessions is renamed from "IPsec" to "IPsec RA".
• The check now additionally produces a service which reports the overall number of active sessions (computed by summing over the individual session types).
• In addition to Cisco PIX and ASA appliances, the check now also discovers Cisco Firepower appliances.

This werk is incompatible. Users have to re-discover the services of affected hosts.

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