Updating config file

[svyas113]

Update the config to reflect the following changes:

1. Default profile that user can configure and shows user how to setup the config file

2. Set the default profile to use gemini 2.5 pro as the default llm

3. Database connection string are supposed to be part of a profile

4. User should not be prompted to select a profile if only 1 profile is available

5. If API key or db connection string are missing, provide clear instructions on updating the profile in the config file telling the user, the profile name and where exactly to find the config file