Add MindsDB SQL Support for CREATE, UPDATE, and DROP Agent

[tmichaeldb]

As part of our LLM Agents design we need SQL support for creating, updating, and dropping agents.

Example Usage

Create

CREATE AGENT my_agent
USING
model = 'chatbot_agent',
skills = ['test_skill']

Update

UPDATE AGENT my_agent
SET
model = 'new_chatbot_agent',
skills_to_remove = ['test_skill'],
skills_to_add = ['production_skill']

Drop

DROP AGENT my_agent

[ea-rus]

Looks good.
There is one error in chatbot test, I think because 'agent' is keyword now