fix(backport): Rename rocks name field to match rock directories from #72

[orfeas-k]

• Rename api-server rock name field to api-server from kfp-api
• Rename persistenceagent rock name field to persistenceagent from kfp-persistence
• Rename visualisation-server directory to visualization-server (with "z" to match naming everywhere else)
• Rename visualization-server rock name field to visualization-server from ml-pipeline-visualization-server

Ref #65