docs: Add sample code

[mwien]

This PR adds example code that showcases usage of the SDK by exposing HTTP endpoints via a FastAPI application. Similar sample code exists for the other two AI SDKs.

This is a draft PR. The architecture/integration of the sample code may be up to discussion and more features should be added.

Currently, examples are included for the following services:

• configurations/deployments via the core package
• native clients (OpenAI/Google/Amazon)
• orchestration

The following additions are planned:

• LangChain
• Grounding
• Prompt Registry
• RPT Models

Open things/questions up for discussion:

• Should the sample_code package be part of the root workspace? This is how it is currently proposed. It would be useful for using it for end-to-end smoke tests.
• I had to add a pyrightconfig.json to the sample code repo for Pyright to find the base, core and gen packages. Maybe there are better solutions.
• Currently, each example is completely self-contained (to make it easy to understand and try out for beginners). However, therefore a new OrchestrationService client is created for each orchestration request. How should the correct cleanup look like (for example with regard to the close_http_connection method, which only closes the sync client)?
• There are some minor type errors from the type checker that one could look into.