Modify the initialization condition in `azure/init.go` to allow the
`openaiModelMapper` environment variable to be optional. This change
facilitates configurations where the model mapper is not needed, and
improving flexibility.
Resolves: #95
* 🐛 set `api_base=/v1` as default value
* 🐛 fix EndpointUrl=nil when `InitFromEnvironmentVariables`
* ✨ add notebook examples
* 💚 fix ci err, fmt for log.Fatalf