chapter15: bugfixes and improvements for notebook-rag-vector-databases.ipynb

[bmerkle]

Describe the bug
depending on @koreyspace feedback, this issue might be split into several issues.

there are a few problems in notebook-rag-vector-databases.ipynb
I have already prepared a PR and fixes for the issues below

• !pip install should be %pip install

• pip install azure-cosmos is missing the %

• az cosmosdb create statement uses a wrong option -r. This should be -g

• az cosmosedb list-keys is deprecated. This should be replaced with "keys list" option

• all envrionment variables should be replaced with an .env file and code which reads them (based on dotenv)

• data file names are invalid (data/frameworks.md?WT.mc_id=academic-105485-koreyst). The part after ? shall be deleted

• code to append() the DataFrame is outdated and shall be updated to use concat() etc

• Python notebook could be split in two parts
  -- part one: read training data, and create embeddings
  -- part two: the RAG part

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👋 Thanks for contributing @bmerkle! We will review the issue and get back to you soon.