Docs vm connections

[thorinaboenke]

relates to issue #95

Add VM access documentation section

• Adds a new documentation section explaining how to connect to the testbed virtual machines on OpenStack/OVH.
• Covers direct SSH access via the mgmt jump host
• Adds ready-to-use SSH config with placeholder substitution commands
• Adds docs on SOCKS proxy tunneling for accessing internal web interfaces (e.g. ZoneMinder on videoserver) through a local browser.

[mlanger86]

Looks like a comprehensive overview on connection options! Nothing to add from my side.