op-mode: T4179: Add op-mode CLI show virtual-server

[sever-sever]

Change Summary

Add CLI for op mode "show virtual-server"

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4179

Component(s) name

high-availability

Proposed changes

How to test

Configure virtual-server and show virtual-server:

vyos@r11-roll:~$ show virtual-server 
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  203.0.113.111:2222 lc persistent 600
  -> 192.0.2.11:22                Masq    1      0          0         
  -> 192.0.2.12:22                Masq    1      0          0         
TCP  203.0.113.112:2233 lc persistent 600
  -> 192.0.2.12:22                Masq    1      0          0

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[dmbaturin]

Looks good, other than a couple of spelling corrections.