Design and implement a more flexible settings file/ structure

[wuxiaohua1011]

Currently all settings are "mushed" together into one big settings.py in carla_client. The downside is that to maintain seperatbility of Agent and Carla, I have to pass in each setting individually to the Agent class, which can be very tedious and lead to incompatibility in the future.

I think we should go with having a carla_settings.py and an agent_settings.py in which both of them contain PyDantic models of settings (so that we can take advantage of the Field(default= xxx feature and serialization to JSON feature.

• implement carla_settings.py
• implement agent_settings.py
• export the settings out to a json to see if users can just modify the JSON to change some parameters.