Improve function io type checking

[jenniferjiangkells]

Addresses #30

CHANGES

• Renamed DataGenerator to CdsDataGenrator - as the behaviour is highly specific to CDS FHIR generation so we might add other types of data generators.
• Refactored OutputDataGenerator to CdsFhirData in models/data with default empty dict for context field and renamed resource field to prefetch for consistency. Also set default model_dump behaviour - exclude_none=True, exclude_unset=True, by_alias=True
• More explicit function I/O in usage for service and client functions:
  • ehr client must return CdsFhirData Pydantic model
  • service takes in CdsRequest Pydantic model (although through type hinting it can also dynamically convert this model to str or Dict, but it's more of a fallback as it's better to keep consistent and use the pydantic model)
  • service returns a list of Card Pydantic model (if a single Card is returned, the wrapper will put it in a list)
• Updated documentation
• shorten sandbox id in save name

Tasks

• Make service func io more explicit
• Make client func io more explicit
• Raise errors to check correct data type is being passed
• Update documentation