PromptFlow pipeline runs on outdated, fixed version of the code

PromptFlow pipeline runs on a hardcoded, statically built Python wheel. See the Dockerfile and
the wheel committed directly to the repo.

This effectively means that no new features and bug fixes are available in the PromptFlow pipeline since December 13.

Attempt to build and update the image used on PromptFlow also does not work, since the codebase now runs on Python 3.11 (see https://github.com/microsoft/rag-experiment-accelerator/pull/2740), but the base image for the PromptFlow pipeline (mcr.microsoft.com/azureml/promptflow/promptflow-runtime:20231207.v2) only supports Python 3.9

In this bugfix, an approach should be implemented to automatically build a new version of the rag-experiment-accelerator library, rather than hardcoding a fixed version.

Start with promptflow/rag-experiment-accelerator/custom_environment/Dockerfile and inspect the committed rag_experiment_accelerator-0.9-py3-none-any.whl. Check how the PromptFlow runtime image is built and how its Python 3.9 constraint interacts with the codebase's Python 3.11 requirement. Done means the PromptFlow image automatically receives a current library build rather than the fixed committed wheel, with the image build working.