Update Agent against volttron-client 3.8

[bonicim]

• Refactor agent to use volttron-client's vip_main to create the Agent
• Update Agent configuration's and constructor
• Add documentation to VolttronOpenADRClient classes
• Update README
• Update pyproject.toml. poetry.lock

[bonicim]

I have made all requested changes and retested the agent on both modular Volttron and monolith Volttron (develop branch).