Self-hosted models: create documentation index locally

What does this MR do and why?

Changes the script to create the documentation index:

• Makes uploading to package registry optional
• Makes downloading the documentation optional, defaulting to generating it locally

MR acceptance checklist

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Before	After

How to set up and validate locally

1. Install requirements:

   pip install requests langchain langchain_text_splitter

2. Run the script generating from local branch:

   python3 scripts/custom_models/create_index.py -o ~/docs.db 
   sqlite3 ~/docs.db "PRAGMA user_version;"
   # 1

3. Run the script generating from local branch:

   python3 scripts/custom_models/create_index.py --version_tag="v17.0.0-ee" -d -o ~/docs.db
   sqlite3 ~/docs.db "PRAGMA user_version;"
   # 1

4. Run the script that downloads a version and uploads to a repository:

   GLAB_TOKEN=<api_token> python3 scripts/custom_models/create_index.py --base_url="http://localhost:3000" --project_id="19" --version_tag="v17.0.0-ee" -d -u