Agent upgrade bug : config unmarshalling

[Alexandre Lamarre]

Steps to reproduce

• Install a gateway in main (commit id : b76f51c6529ce3ea760ac70c72cf5d735248ed79 as of writing this)
• Install an agent in the local cluster with version v0.10.0

Hits errors related to unmarshalling config files for agents

2023-06-26T17:18:17Z INFO commands/agent_v2.go:65 using config file {"path": "/etc/opni/config.yaml"}
2023-06-26T17:18:17Z ERROR config config/config.go:53 error loading config {"documentIndex": 0, "error": "failed to decode object: error unmarshaling JSON: while decoding JSON: json: unknown field \"pluginDir\""}
2023-06-26T17:18:17Z FATAL commands/agent_v2.go:79 no agent config found in config file

[Alexandre Lamarre]

Expected failure, upgrades will have to be done manually for downstream agents in 10.1