Refactor agent create assistant api

[lkk12014402]

Description

1. instantiate agent when request http://${ip_address}:9091/v1/assistants
2. allow user to config agent through api call

related to this #982

[lkk12014402]

test

curl http://${ip_address}:9091/v1/assistants -X POST -H "Content-Type: application/json" -d '{
     "agent_config": {"llm_engine": "tgi", "llm_endpoint_url": "http://10.7.4.56:8085/", "tools": "/home/user/comps/agent/src/tools/custom_tools.yaml"}
    }'

curl http://${ip_address}:9091/v1/threads -X POST -H "Content-Type: application/json" -d '{}'

curl http://${ip_address}:9091/v1/threads/thread_5c36add6-3318-45a0-828a-b4df8b486b54/messages -X POST -H "Content-Type: application/json" -d '{"role": "user", "content": "What is OPEA project?"}'

curl http://${ip_address}:9091/v1/threads/thread_5c36add6-3318-45a0-828a-b4df8b486b54/runs -X POST -H "Content-Type: application/json" -d '{"assistant_id": "assistant_ReActAgentLlama_19da8466-8d61-4846-8ecb-732ae2d65646"}'

[minmin-intel]

Can you please update UT with the tests in your screenshot?

[lkk12014402]

Can you please update UT with the tests in your screenshot?

update ut script